A bit of a repost of a guide I already posted in discussions, but I hope this'll help some of you in getting pointers on how to achieve the Flawless run. By no means a pro guide, but if I managed to get it with this, so can you!

As far as difficulty go, ironically, Overdrive 5 is a lot easier than Overdrive 0. That 200% XP modifier more than makes up for the increased horde, HP, and enemy speed. It's the difference between getting rammed into by a fish (screw them) and sitting in the middle of the screen firing more missiles than a whole season of mecha anime.


With the Contamination Update out, a lot of the info on this guide has been made obsolete as better methods have been found, and a lot of gameplay changes made the old tactics not as efficient anymore.

With this guide, you too may achieve the Hitless run with relative ease. And we'll start by setting the difficulty to an overwhelming Overdrive 0. Thanks to a lot of weapon buffs, the lack of XP from higher Overdrive levels is balanced by how the raw power of upgrades can do a lot of the heavy lifting, combined with the power of the new Suits.

Of course the loadout is going to be important, but quite frankly, only a few skills are necessary to give you a good chance of getting a Flawless run. Here's my recommended loadout, and the reasoning behind it.

Be aware that this was done with 30 Skill Points in mind. Any less and I cannot guarantee how well this'll work. If you Prestiged your profile a few times and got up in some Overdrive levels, it's significantly easier, but by no means necessary.

Spaghettification: Gives you back one black hole after a boss is defeated. Not necessary if you consistantly prioritize Black Hole Drills, but not a bad upgrade either. Trade this for a Ban or Reroll if you don't want it.

Salt The Wound: 10% damage on anything under an elemental effect. This'll come in very handy, as elemental effects (read: shock) will be crucial in making the run a lot easier through crowd control and the extra damage.

Battery Lick: A must have to make this run easy, and honestly you should always have this upgrade no matter what you're going for. Shock is by far the best elemental effect in the game, able to freeze enemies in place and deal high damage at the same time. It may only be 1%, but since we'll be firing tons of projectiles at once, it'll make a difference.

Remnants of What Was: Statues are not really useful in our run, in fact some of them are actively detrimental if they raise Curse, same if you blow them up with a Grenade for a free level up, but we need this skill to get the drills. Curse is to avoid at all costs, so refer to this guide for a list of existing statues and their effects: https://cs2bus.com/sharedfiles/filedetails/?id=3114710211

Driller Enhancements: An excellent skill that'll go a long way in helping you getting that Flawless. With the new update, Blackhole enhancement drills are by far the best ones as they provide you with a panic button that you'll most likely need in early Mortality.

Marathon: Temporary movespeed on kills. This'll save you a lot of close calls during levels, as movespeed is going to make the difference here. Even without Overcharged Engine, this alone really helps keeping you ahead.

Exponential Expedition: Movespeed based on Mortality. Movespeed being a pretty important part of the build, it's a must have.

Confidence: A great skill that'll play right for our build, as we'll want to maximize our agility. Gives up to +15% Move speed as long as you don't get hit.

Bullet Time: A bit of a crutch if some patterns stress you out, but it can come in handy in case your DPS isn't high enough to one tap the bosses yet.

Magnetosphere: Boosted XP Radius when using a Black Hole, it's not super useful for us but necessary to get what we actually want. Comes in handy in case you're in a tough position and had to panic Black Hole to avoid getting hit.

Exponential Experience: Pickup Radius will make it a lot easier to level up while you're being chased down. It's guaranteed increase as the game goes on, so you don't have to spend a lot into Pleoxenic Crown to get a decent pickup radius size.

Shocking Results: Free upgrade at the start of the run and after every boss. Very important to get the ball rolling and compensate for the lack of DPS early game.

Expert: +5% XP Modifier. Most of our build relies on stacking as much weapon upgrade as possible, it's very important to have this.

Black Atomization: Drags anything on your screen into your Black Hole, clearing enemies that may be too close for comfort. A good way to clear the screen, and necessary to pick for the following skills.

Fast Core: Makes your CORE bullet go faster, and thus more accurate. Handy for triggering Shock early game.

Stack Overflow: A guaranteed "crit" every 100 kills.


Hunting Season: Another mandatory one. -20% Boss HP (yes actual %, not the % you see on screen), I don't need to explain further.

Feeling Lucky: 1% of crit makes a lot of difference. It simply chews up hordes when you have fast-firing weapons triggering crits over and over.

Rainbowsplosion: A guaranteed chain grenade on an Elite kill. Excellent for wiping out a horde, and clear a path toward whatever the Elite left behind. Not necessary by any means, but I keep it for peace of mind. You can trade this for an extra Reroll or Ban if you want.

And whatever points left you have you can dump evenly into;

Rerolls: Necessary for dropping the items we actually want and get the ball rolling. Rerolls all 3 upgrades on the level up screen per use. Can also be spent on the Gambler Statue in exchange for Level Up disks, in case you already have all your necessary upgrades.

Bans: Get rids of an item in the selection list, disappearing from the possible pool of upgrades for the run. It helps to "thin the deck" and more chances of getting what we want from Rerolls.

Both Bans and Rerolls reset after every Boss.

With the new Contamination update, Suits have been added to the game, giving you a different starting weapon, stats, and sometimes passive effects.

For our purpose, only one suit is really what interests us, and is the humble


OPTIMIZED. Suit.

Why this suit in particular, you ask?

It starts off with Core and only 4 Max Slots. For some, it may sound like a bad deal, but it's why this suit is one of the most powerful in the game in my opinion; once you filled up your slots, you're always guaranteed to roll one of your main upgrades on level up.

I mean look at her, even she knows this suit means business.


There's also a case to be made about the PERFECTED. Suit, but I honestly cannot recommend it as the even smaller Max Slots and XP radius makes it more sensitive to RNG for little reward and forces you to take more risks to pick up XP, while the OPTIMIZED. Suit brings just as much power and gives some wiggle room to slot in a "whatever" upgrade in case the RNG is being mean to you.
It's also super annoying to unlock and you need the OPTIMIZED. Suit for it anyway.

If you haven't unlocked the OPTIMIZED. Suit, you have to finish a run with 4 or less items. It's not that hard to achieve; max out your Bans and Rerolls on Overdrive 0 and pick the same core weapons as this guide while consistently banning everything else, you'll be done in no time.

With the Contamination update, a LOT of the weapons went through a bunch of buffs, and some of them are strong enough to carry the entire run.

For this run, you'll be banning and rerolling upgrades until you get at least two out of these three upgrades:

Missile Rack: Absolute monster of a weapon that can wipe hordes and bosses all on its own. Stack enough of these and you turn Cyl into a SAM launcher on steroids, deleting anything that dares to peek around your screen.




Static Satellite: Static Satellite is the boss melter. Stacking Static Satellite means that all shots rain down on the boss at the same time. In other words; this can easily delete bosses before they even get to use a single attack.




Digiwatch: Cooldown reduction for making your weapons fire faster. With a high enough Cooldown% (200% is more than enough, but you can go up to 300% if you want), you'll be safe from everything except your own hubris if you decide to get cocky and get hit by a stray bullet.




Missing Reward: While not as immediatly powerful as Digiwatch, the Missing Reward brings a lot of value to the table thanks to providing a %rate of Poison, Slow, Shock and Burn. Meaning you can trigger any of these effects, on top of bringing Pickup Radius, Cooldown Rate, Weapon Scale and Projectile Speed, making the Missile Rack much more efficient if you can pair it with. Not as recommended with Static Satellite.

• Don't rely too much on autoaim! While Missile Rack and Static Satellite don't need you to do much work, it's useful to keep an eye on priority targets like debris that you could be aiming at and potentially score an item off of, or some extra XP.
  
  
• If you're surrounded, don't forget to use Shift if you have Bullet Time, making it easy for you to see through the crowd and get out of a tight spot.
  
  
• Don't be greedy with black holes! Black Holes are your panic button. If you you're getting overwhelmed, don't be afraid to spend one to avoid restarting a run. Not to mention you can rather easily find some in floating debris, or left over by sparkling elites. Remember that you'll always get one back after every boss if, and Picayune drops one after every phase if you picked Spaghettification, and all the Black Hole Drills upgrades will leave you with more than enough to spare.
  
  
• Pick your routes well. You'll want to avoid Modified areas at all costs (except the Horrific Force, this one is easy to deal with), and pick your battles. Remember that enemy types are added to the pool of spawned enemies, so pick those you know you can deal with. Anything with high mobility can become a real threat, and any enemy able to shoot at you is extremely dangerous. Avoid things like Warpers, Snipers, Droids, or Lob, for example.
  
  
• DO NOT GET CURSED. Curseformed enemies are supremely dangerous, can, and WILL ruin your day, especially Hands and Fish (screw them). To this effect, avoid interacting with statues you know will raise your Curse, or try to blow up any of them for a free Level Up as it'll raise your curse.

Note that if you're following this guide, you probably won't even get to see half of these attacks as they'll be dead before they even show most of them! But for the sake of the old version of the guide and being thorough, i'll leave this information here.

Rabbit

The easiest of the bunch. Rabbit doesn't require a lot of strategy, simply focus on dodging and the boss will go down rather quickly, even before it can loop around its bullet patterns.

The big rings are easily avoided by going in the gaps between them. Moving away from Rabbit while aligning yourself vertically can make it a breeze.

The pattern of vertical bullets is also easily avoided if you go slightly left or right from the center, there's a very obvious gap where you can stay and avoid getting hit. Feel free to use Bullet Time (sneak) if it's too fast.

The "labyrinth" is also an easy one, extra easy if you're playing on a controller since you can adapt your movespeed to the bullets.

Worm

Worm will start to test your mettle a little bit, but not too big of a challenge. With your movespeed upgrades, you can easily avoid the charges. If possible, try not to break it apart and focus on the head, as it'll be more easily manageable this way. Don't use autoaim. Remember that Shock will freeze the whole boss if any part is hit by it, giving you an easy way to maneuver around it.

Be careful of where the boss drops the static green bullets, you don't want to get caged in when it fires the homing yellow ones, or the burst of blue ones. Keep your distance and enough space for you to maneuver.

Biker

Biker is the first real "build check". If you've been able to defeat Rabbit and Worm with ease so far, Biker shouldn't be too much of a problem as long as you have enough move speed. Even without Overcharged Engines, you can flee from Biker forever with all the loadout upgrades! Simply go for a diagonal direction (to avoid the cross-shaped bullets) and stick to it, pay attention when you hear Biker rev up as that means he'll go for the charge, which can potentially catch up with you.

Demon

Ironically, the boss with the lowest self-esteem is also the biggest threat of your run. With fast, intimidating patterns and the ability to teleport, this can ruin your run if you don't pay attention. We want to get rid of her as fast as humanly possible to avoid the more problematic patterns or worse yet, let her loop around them.

Unfortunately, movespeed won't let us cheese the boss like Biker. It's the opposite, in fact; going too far will make the boss teleport to you while she keeps firing, which will definitely put you in a bad spot. You have to stay far enough away that you can easily dodge her bullets without triggering a teleport.

Bullet Time will come in very handy here, especially with the grid-like bullet patterns, or the very first pattern she fires, allowing you to tap-dodge while sticking to the outer rings of her bullets, much easier to handle. Be careful when you see her fire a ton of bullets in two directions; stick as close to her as possible so you can avoid the wall of death, and watch when her bullets curve around to come back to her. She also has a wave of slightly homing yellow projectiles like Worm, but her bullets spread across the whole screen. Bullet Time is your friend here, or a Black Hole if you miscalculated.

Picayune

The home stretch. Three phases, and thankfully we get a Black Hole pickup after phase 1 and 2.

Phase 1 and 2 are not too different from one another, as they're basically the same patterns you've seen from previous bosses. Picayune also follows you around, so don't be afraid to keep moving and run away from her bullets. By now, you should have enough move speed to run circles around Picayune and her bullets.

Phase 3 is where you should keep a couple of Black Holes in your pocket. Most patterns are easily avoided, but one where she laughs and sends you walls of bullets from your left and ring is where you NEED a Black Hole to avoid getting hit. Thankfully, that also gives us a ton of extra bullets to fire in her face.

If you've managed to get your hands on some Black Hole drills, this boss should be pretty easy. Try to maximize your damage whenever you get a window of opportunity, so we don't let her loop around her pattern too much, you don't want to get caught in a Wall of Death with no Black Holes left.

If you've followed this guide and had a little favor from the Government Upgrade Slot Machine, you should see pretty quickly how you're wiping the floor with any spinning cornchip that dares look at you funny.

I've managed to reproduce this tactic fairly reliably, you can even complete a hitless run with only two upgrades as you can see here:



You can go Hitless pretty high in Mortality with this build due to how strong it is, all the way to the Mortality 50 boss.






That's about it! Now you can get the Flawless achievement with ease. Hope it helped you!

Thanks for reading!