These achievements will unlock naturally during gameplay over time

Score total of 100,000 points in story mode

Score total of 200,000 points in story mode

Collect 1,000 stars

Collect 8,000 stars

Collect 15,000 stars

Some of these will unlock naturally during gameplay, others might require finding a specific place to fight a specific monster, in order to unlock an achievement

Find 10 secret stars, Find 50 secret stars, Find all 100 secret stars.

finding 10 and 50 stars will come naturally during gameplay. you might even find all 100 if you're exploring for them and not speedruning or rushing to finish levels at hardcore difficulty.

my first playthrough was hardcore (more details later in this guide) therefore i did not spend too much time exploring for the stars.
i completed these achievements in my second playthrough. i chose kid difficulty, which means you are absolutely immune to the monsters and the environment (you cannot die in any way shape or form). i explored every single level and found all 100 stars easily.

Complete a story level without taking any damage

play the first level on easy/normal difficulty. avoid enemies when possible or go for safe kills. be careful of the enviroment and take your time, don't rush. complete the level without taking any damage and the achievement will unlock. if you took damage, restart the level. this shouldn't take too long to complete.

Complete a story level without killing any creature

play the first level on kid difficulty. avoid all enemies and complete the level. you can't take damage from the enviroment, so dont worry about getting hit by spikes in order to avoid hitting an enemy.

Complete a story level in less than 5 minutes

play the first level on easy/normal difficulty. avoid the enemies and be careful of the enviroment and just rush to the end. very easy to achieve.

Kill 10 enemies using another enemy

this one is pretty simple. stun an enemy by jumping on their head, then punch them in the direction of another enemy and get the double kill. repeat this 10 times.

Kill 5 enemies by bouncing from one to another

this achievement requires performing a chain kill of at least 5 enemies, by bouncing from one to the other. there is another steam guide that covers where and how to complete this achievement: http://cs2bus.com/sharedfiles/filedetails/?id=219330390

Punch 100 enemies

easy enough, stun enemies by jumping on their head, then punch them

Kill 100 enemies using stomp

Kill 10 enemies using a falling rock

certain maps have rocks that can be dropped by a super stomp. use them to kill 10 enemies.
there is another steam guide that covers where and how to complete this achievement:
http://cs2bus.com/sharedfiles/filedetails/?id=422956563

Kill a hedgehog

at first it is impossible to kill a hedgehog but later on there is a trick to get this achievement.
there is another steam guide that covers where and how to complete this achievement:
http://cs2bus.com/sharedfiles/filedetails/?id=219305469

these will take some time and patience to achieve. here's how i got them.

I chose to play this game on hardcore difficulty from the start. it gave me no comparison of what the easier difficulties might be therefore it was the only difficulty i knew, and it wasn't too hard to complete. It also allowed me to obtain all 3 difficulty achievements at once. i also only had to finish the whole game once.

it took about 20 hours to complete this over a few days, sometimes with long breaks in between.
the first levels are pretty simple and so is the first boss. if you find yourself having a hard time, make sure you complete a level before closing the game, otherwise you will have to repeat the level again from start (level, not full chapter.)

i used youtube a lot for this, whenever i got stuck and didnt know how to progress, i looked up some gameplay and watched how to pass the obsticle. i also watched boss fights over and over and learned the pattern they use, and in time i managed to defeat them all.

by doing this I unlocked 100% easy, 100% normal, 100% hardcore and Final boss defeated all at once.

if you want to make this experience a bit easier, avoid trying to find the secret stars by exploring, and just go towards the end of the level. you can obtain the secret stars achievements in another method which i have explained in this tutorial as well.

First boss defeated, Second boss defeated, Third boss defeated, Final boss defeated

if you choose to play this game in kid/easy/normal difficulty then this should be pretty easy to achieve. the bosses are harmless in kid difficulty, and a little bit more challanging in easy/normal difficulty.

If you choose to play the game in hardcore difficulty, do some research before killing the bosses. first try to learn the pattern in which the boss attacks. if you die too early you can search for the boss fights videos online, i watched many youtube videos to unlock this achievement.

also, be patient. this might take time but its doable. if i could do it, anyone can. (and i raged a lot at this!)

this game was very fun to complete. although the hardcore difficulty might be exteremly frustrating at times, it was well worth it in the end.

i didn't cover the arcade and challange achievements because i have yet to complete them. if i do and i find some useful tips, i will add them here.

enjoy!