In order to access the DLC and start the trinket hunt, you first have to go to the mailbox ouside your cafe and interact with it to get a note from your aunt.

The mailbox only spawns after the initial tutorial is over, so you do have to listen to Kiva and follow her instructions before it will appear and allow you to get it.



Once you interact with the mailbox, you'll receive the letter, which will be placed in a box with the silhouettes of the other trinkets. This is where you can check them for clues to their location, as well as checking how many you still need.




If ever you want to check this box, it can be found with all your other quests. On keyboard and mouse, you access the quest list by pressing 3. On controller, you use the right arrow on the D-pad.

Hint: There's a magic cat grove near the cafe where all your cares can float away.

If you stand in front of your cafe, facing it, go down the hill to your right, towards the cat glade that eventually leads to the Witching Woods. On one of the small pink platforms at the base of one of the trees, you’ll see a bubble wand and a little bottle of bubble fluid. Pick up the wand and press the use button to blow bubbles. After a few seconds (and blowing a massive bubble) you should add it to your collection.

Hint: Oliver is a well known connoisseur of useless junk.

When heading into town, if you go behind the clothing and furniture shops, you should find Oliver the cat standing at a dumpster (he can be in a few other areas, but before opening any other areas this will be the most consistent place to find him). He sells the Bottle Cap for 1000 beans (yes, that is the currency name).

Alternatively, there is a waterfall that is visible from the cafe where, going behind it, you will find Oliver's home, where you can also access his shop.
Oliver is also where you will get the Cat Potion and Remote Controlled Mouse you will need later for Things in Cutie City and Golden Grove.

Hint: Luckily, rain washes away magic accidents

Head up to Autumn's home (that's the large potion bottom atop the hill in town). Once there, talk to her to access her shop and buy yourself the Rainy Day Potion.

After buying the potion, leave her home and return to the base of the little mountain she lives on. Run around the perimeter of her hill and eventually you'll come across a blue mushroom and a suspicious bright orange puddle.

Access your inventory, go to potions and use the Rainy Day Potion over the mushroom. It will quickly grow pretty big and reward you with a smaller mushroom for your collection.

Hint: If you see a rain cloud, you should always be ready to make a splash!

The Mirror is one of the only two items that can be gotten in any of the areas.
At any point during the game, you might see a large, grey rain cloud slowly drifting around (I saw the one pictured here drifting across the Clover Coast while I stood in Heart Village, at the literal beginning of the game).

The objective is to jump in the puddles left behind by the cloud. Once you jumped in 3 of them, you'll receive the mirror.

Hint: A snowball fight can start when you least expect it.

As you climb up Snowbell Mountain on your way to the Onsen, you'll stumble across a little cat-like snowman (it's in the exact same area as the polar bear family).

Pick up a snowball from the pile next to it and use it while facing the snowman (Left mouse button on keyboard and mouse, X on controller). If you manage to hit the snowman, its hat will fall off and it will declare that "Oh ho ho! You caught me!" After which you will receive a stick.

Hint: Snow friend isn't very good at games, but they still like to play.

Before starting up the path that leads to the Onsen, take the path leading to the right.

Keep following this path until you reach an open section of snow, where you will find Sugar and another snowman, this one with a tic-tac-toe board built out of sticks.

Now just play tic-tac-toe with the snowman (it seemingly will always make the worst moves). Once you beat it at the game, it will give you a piece of coal.

(You can also replay this by walking up to the snowman and resetting the board.)

Hint: Snowballs start small, but they can really grow on you.

Once you reach the Onsen, check the snow outside the front door (where Harvey is chilling) to find a tiny, fully white cat in a snowball.

Now, start rolling the cat around by running into it. It will slowly start to grow in size. Keep pushing it around, it takes a little while for it to fully grow.
Once it is at full size, it will explode into a shower of snowflakes, giving you the carrot that was its nose.

Hint: Support your local dance troupes!

Shortly after entering Cutie City, in the second street from where you enter from the mountains, you'll find a cat breakdancing on a dance floor made of cardboard. Walk up to the hat next to this cat and start donating beans.

Donating beans causes the cat to spin a little faster every time. Keep donating beans until the cat starts lifting off of the ground.

Once it reaches adequate height (for me this cost about 10 beans, so donating 10 times), you will receive the mixtape.

Hint: Just what exactly goes on in the cat corp offices?

Two streets down from where the dancing cat is, you'll find a green building with Safeena and a bunch of business cats outside of it.

Enter this building and ride the elevator up to the top, where you will find the cat corp office. Once here, turn to the left wall and walk up to the photocopier (it has a blinking red light).
Use the photocopier and after a few seconds you will receive the photocopy.

Hint: Every animal wants to ride the plane, but they would feel better if you joined them

Once outside of the cat corp building, head directly down towards the pier to find two small airplanes.

Pick up whatever small animal companion you have with you in your party (or just grab one from nearby). I used Ms Kitty, who naturally walks around this area, but you should be able to use any animal that is small enough (I would maybe not recommend using birds since their models clip a lot, but they should still work fine). Carry your friend to the smaller airplane and interact with it to place them inside.
Once your companion is in the small airplane, walk up to the bigger one and interact with it to get in yourself and go on a flight with your friend. Once the flight is complete, you will get a toy airplane.

Hint: Beat the first level of Mama Cat's Crossing

The purple building on the pier close to the airplanes is the arcade, where you will find Mama Cat's Crossing, an arcade game where you basically play Frogger.

The inputs have some slight latency, but once you beat the first level, you can exit and receive your teacup.

Hint: Beat the first level of Mama Cat's Parade

To the right of Mama Cat's Crossing, you will find a second arcade game called Mama Cat's Parade, which is a little like Snake.

Once again, there is slight input latency, but luckily you only have to beat the first level before exiting and getting your tickets.

Hint: Only a claw machine master can grab the ultra rare cat plush

Upon exiting the arcade, walk around the right side (if your back is to the building) to find a claw machine.

Inside, among the cat paws (beans) and some furniture you can win, you might spy a familiar calico coat.

This is the prize you're playing for.
The claw only costs money to drop, not to move right and forward, so take as much time as you need to properly line it up before paying 25 beans to drop the claw.
If you manage to catch it and get it out of the machine, you will be rewarded with both a token and a new animal companion: Plushems.

Hint: All away around the bar? Is it really possible?

At the very top of the city, next to the ramp leading up to Heart Village, you will find a little playground.

Walk up to the swing and interact with it to sit down. Now, using either your left joystick or W and S, you're going to start swinging back and forth.
Keep swinging and going higher and higher. Eventually you will swing fully 360 around the top bar of the swingset and receive the yo-yo.

Hint: Both humans and animals enjoy Cutie City's playground.

In the playground, climb up the little jungle gym with the yellow stairs.

Walk over to the slide attached to it and, by just walking forwards, slide down it to receive the shovel.

Hint: They say there's a secret bar in the city that only cats can go in.

Before doing anything else, make sure to grab the Cat Potion from Oliver. You cannot progress without it. He does not seem to have it from the very beginning of the game, so maybe try sleeping if he doesn't have it.

After getting the potion, head back to Cutie City. Once here, while standing in the same street where Xin's house is, you can see a small alleyway and a pink building with a slot in the door where (if you look carefully) you can see some eyes peeping out.

This is where you're trying to go.
Once outside the door, use the Cat Potion to turn yourself into a cat. Once you are a cat, go up to the door-cat and talk to them. They will ask you a password and once you respond, you will be let in.
Walk through the door and talk to the bartender, who will give you the scratch book.

Clover Coast has some of the more convoluted things to collect, with two that require you to head to other areas to start getting them, one that requires an animal from a different area and one that requires more than one trip back to your cafe.
So let's start with the only one that is contained to the area.

Hint: Seeds on the wind

Upon reaching the Clover Coast, look around between the flowers until you find one that looks almost like a ball on a stick.

This is a dandelion.Walk up to it and pick it up.
Once you are holding it, use it, presumably blowing on the dandelion until the stem is empty.

Hint: The local creek tends to get filled with debris after a big storm

Now, to the quests starting elsewhere.
Starting from your cafe, head to the waterfall Oliver lives behind. Right outside it, you'll find some debris in the water, along with a rubber ducky with cat ears.

Get in the water and interact with the debris to remove it and let the ducky pass. Now, follow the ducky on its journey down the stream, removing any debris that might stop it again. You can do this by either running along the shore of the stream or by swimming along it with the ducky (swimming is slower, but it will make it easier to track the ducky once it reaches the coast itself).
Eventually, the ducky will reach its family, with one large rubber ducky and three other smaller ones.
Swim up to the family and interact with them. They'll swim a little distance around you and you will receive the rubber ducky.
The duck family is right outside Nahla's cave, so if you haven't met her or are unsure where to find her, this is a great chance to do so. You'll need her help for a thing in this area.

Hint: The peak of the mountain offers you a bird's eye view

First and foremost, get a bird. My usual bird of choice is Poe, though in this instance I decided to use Hoots, since you can find the white owl on your way to where we're going.

After grabbing your bird of choice, head all the way back up Snowbell Mountain and through the Onsen. Once past the pools, head right, following a slightly obscured path that leads to a large cat bell and some stairs.
At the top of the stairs, you'll find a sign, depicting a person being seemingly carried by a bird.

At this point (if you haven't already), take your bird and store it atop your head (while holding the animal, use right mouse click on keyboard and mouse or B on controller).
Interact with the sign and it will spawn rings in the air. Now, WITH YOUR BIRD ON YOUR HEAD, jump off the mountain to glide through the hoops.
Remember to press forward to get some extra speed, otherwise you might sink too low to reach the hoops. It does seem like you get sent back to the start if you reach the ground without gliding through all of them, so no worries if you don't get it right the first time.
Once you reach the ground in Clover Coast, having gone through all the hoops, you will receive a feather.

Hint: Every dog deserves to be pet!

Behind(ish) the lighthouse on the coast, overlooking the sea, you'll find a dog statue.

Walk up to the statue and pet it. This is done by pressing E on keyboard or RB on your controller. A part of the dog will get visibly shinier and you'll get a prompt to come back on a different day.

Go back to your cafe, sleep and return to the statue. It should now have changed, with the dog laying on its back for tummy rubs.

Pet the statue until its tummy shines and promps you to come back on a different day again. Go to the cafe, sleep and return again.
Upon your final trip to the statue, you might notice it is now entirely shiny and also moving.

Walk up to the statue, now a dog named Brawnzy, and pick them up. You will immediately be given a key.

If at any point you return to the statue and it did not change, exit to the main menu and try again. This has only happened to me once, but exiting will fix the bug and allow you to try again.

Hint: Nahla is looking for a cat with the face of a manatee, the ears of a dumbo octopus, the legs of an elephant, and the physique of a baby seal (only available after asking about her studies)

Upon meeting Nahla (or maybe after coming back to talk to her again), ask her how her studies are going. She laments not being able to find a very specific animal, the entire reason for her coming to the island to begin with.
The animal she's looking for is Pudgems, who can usually be found wandering around Sunny and Blossom's houses. (Alternatively, if you have picked him up before, you can use the animals tab to assign Pudgems to your party for easy access).

After finding Pudgems, grab the manatee-octopus-elephant-seal cat and make your way back to Nahla. Holding Pudgems, talk to Nahla, who will be delighted and start taking notes.
After a short conversation, she'll agree to come to the cafe some time and give you a shell.

Hint: Check out your local tiny library

Enter Golden Grove from the Clover Coast, crossing the wooden bridge. From there, follow the path in front of you until you reach a fork, from which you go left until you see what looks a little like a birdhouse.
This is the tiny library. Walk up to it and interact with it and you will be given a popup book.

Hint: It's nice to have a soft landing

As you make your way through the Grove, you'll begin to notice piles of leaves laying around.

Jump in 3 of these piles and you'll be given a cool leaf.

Hint: Unable to deliver package of cheese: building was too small for a human

First and foremost, make sure you have the Remote controlled mouse. It's available in Oliver's store.

Once you have the mouse, return to the Grove and head to Daisy's house. A little past that, you'll see a stump that is much darker than any of the other trees.

Open your inventory, go to the Toys tab and choose the mouse. Now use Q (keyboard and mouse) or LB (controller) to deploy it and head into the mouse hole in the stump.

Once inside the stump, you'll see there's a little maze you have to do. Make your way through the maze until you reach the mice in the middle, who will give you a paperclip.

Hint: There's a thief stealing neat things from the other animals! Last seen in the north east of Golden Grove

Starting from the back of Gabby's house, head down the little hill to find a tree with some junk scattered around its base.

As you run around this tree, you'll catch a glimpse of it's elusive resident, Lil Grabbers. Chase the raccoon around the tree until you can grab it.

Now that you have Lil Grabbers, it's time to shake the racoon. While holding Lil Grabbers, use E (keyboard and mouse) or RB (controller) to wiggle the little thief. Things will start falling out of Lil Grabbers. Keep shaking!

After an adequate amount of shaking, Lil Grabbers will drop a bandit mask that is now yours for the taking.

Hint: Identify the unidentified flying object

Once you receive the Portable Broomstick from Rosa, hop on it and take to the sky. Look around until you see what looks like a hot air balloon in the distance.

Fly up to the balloon and speak to the cat piloting it. After a short conversation, you will receive a balloon.
Note that this balloon is not necessarily above the Witching Woods. It's a lot like the raincloud that gives you the mirror, the balloon seemingly floats across the island freely.

Hint: Mix up a potion that matches

Outside of Rosa's house are two cauldrons, one that is smoking and one surrounded by three jugs/vials with a sign next to it. The second is where we want to be.

You'll see there is a sign next to the cauldron with a weird shape on it. Our goal is to add enough of each vial to recreate it.
For example, the square is red and the whole square is there, so add red until the entire shape is there. The blue circle is about 3/4 there, so only add until the blue in the cauldron matches the sign. Same with the green X, which is about half. Since it's hard to explain, I've added more or less how each colour should look.

When they're all added together, they should look a little like this:

Add any colour you don't have enough of, or use the black bottle to remove any excess colour (in my example I had to use black to remove a bit of the green). Once it's close enough to what's on the sign, you'll automatically get the nail polish.

Hint: There's a lonely mushroom with no one to dance with

First and foremost, go to Cutie City and talk to Malcolm to receive the quest Dance, Dance! Follow the quest to its completion and Malcolm will reward you with the Dance Potion you require.
Now that you have the Dance Potion, return to the Witching Woods. From Rosa's house (if you're facing it), follow the path left past Ranger and Tac, stopping before you find Tiny. If you look right, you'll see a single grey mushroom.

Walk up to the mushroom and use the Dance Potion to start dancing. The mushroom will start "dancing" with you, changing colours as it does so.

After a short dance, it will give you the eggshell.

Hint: The fish create bubbles to float and catch bugs, but sometimes they need help getting down, a balloon might make it easier

At the pond where you can find Blumby the elephant, you'll notice some fish seem to be floating in bubbles.

Starting at the bottom, you're going to jump onto the first bubble. It will bounce you up fairly high, after which you will aim for the next bubble down the line, aiming to follow the line of bubbles to the top of the waterfall as if they're stepping stones. The bubbles to the left and right don't matter, just the path of fish from bottom to top.

Once you reach the end, you'll receive a paintbrush for helping the fish.
If timing the jumps proves to be a little difficult, this can also be done by using the Portable Broomstick to fly through the bubbles instead.

Hint: Your collection is pretty impressive, perhaps you can share it with someone that wants to learn about life on the island.

Once you have collected every other thing from every other area, return to Nahla to talk to her. She tends to either be in her cave in Clover Coast or hanging out at your cafe. For me, she was at my cafe.

She'll mention noticing your collection and ask you to show it to her if you ever complete it (this conversation can take place at any time, I just didn't speak to her much before this).
Talk to her again to tell her that your collection is complete.

She'll comment on how neat your collection is and, after some rumination, will thank you for helping her to achieve her goal before giving you the certificate in recognition of your contributions to science.
After a brief comment on how she can't wait to share this with everyone back home, but not before she pets more cats, Nahla will stop talking and you will officially receive a Neat Diploma, the very last of the Neat Things you need to complete your collection!

For help with actually finishing the game, hunting achievements and all the collecting that don't include Neat Things, I recommend looking at this guide (it's what I used for my initial playthrough as well):

https://cs2bus.com/sharedfiles/filedetails/?id=2350002045

I hope this guide helped you along your journey to complete your Neat Things collection! If you have any further questions, please feel free to ask in the comments section.