SUPERHOT

Update 3: This has now been fixed in the latest update so tracking for this and each of the 100 kills achievements is working again

UPDATE: Since the latest update, tracking for this has been screwed up. Each time you launch the game, the tracker will only ever go up by 1. If you quit out and reload, you can get another 1. This means that, currently, only about 30 kills per hour could possibly recorded. Not recommended.

Update 2: ox BlackJack xo received a reply from the developers saying they are aware of this and are working to fix it (See comments below). Thanks BlackJack

EDIT: I noticed someone else posted a video showing how to farm kills on the office level. That way does look quicker than mine. As I haven't unlocked the office level yet (and not sure how many kills I need to do so) I guess I'll use my method until I unlock OFFICE and then switch to their method. The OFFICE farming video is in the solution to the Full Package achievement linked below

Original Post
I don't have this yet, but I just managed to get 310 in one sitting (only stopped there as I was getting bored) so this will be the way I get this

Play the BRIDGE.lvl level. You are wanting to spawn with a katana straight ahead of you. Punch the red dude to death and grab the katana. Head down the stairs behind you, keeping to the left. Rock back and forwards on the bottom few steps to advance enemies. They'll come running round the corner at the bottom of the stairs. Pick them off.

The katana has a surprisingly long range and a very fast "reload" time so you should never get hit. If you hover the target reticule over a red dude and he turns stripy, he's in range to be hit. You should easily be able to get 10 kills per minute from here once they start spawning quicker as your scoe increases.

If you don't spawn in the right place, get shot and try again. I spawned there about 50% of the time before I realised I could farm kills here.

It will also help you progress towards

Nice and easy guide from Davehx.
Just wanted to add a alternative guide and position as I found this much easier and quicker.

Load up Office endless level and find location near the big open vertical windows in the corner just behind the water dispenser.

It only takes a couple of Red dudes to steal a katana from. Once you have this, the grind starts.

Once you have wedged yourself into the corner, line up crosshair half on half off the water dispenser and keep walking forward to make time move. This will keep them coming thick and fast.
This position will also help you react quicker, just make sure you swipe once the crosshair is hovering above a Red dude, you may miss sometimes, but you will be suprised with the reach of the Katana.
Some may deviate out of reach but is fairly simple to walk around and take them out.
As you can see, I hit 400 in one run, this took about 20-25 minutes for 400.

Easy enough to get in to a rhythm, shouldn't take to long at all.
Hope this helps and good luck! :)

For endless mode you will have to kill 1987 red dudes, you can do this across any endless levels, but I would recommend doing it on Bridge, Lobby, Office or Breaking as they are the fastest to grind kills.

There are 9 different levels called LAB#18, STAIRS, BRIDGE, BREAKIN, HALL, LOBBY, WAREHAUS, OFFICE, PWRPLANT each has 4 different modes. Endless, Race, Time and Real.

Endless: The mode you will be playing in, just killing red dudes.

Race: Get 30 kills as fast as possible.

Time: Kill as many red dudes as you can in 20 seconds of in gametime. (Think SPEEDRUN)

Real: Kill as many red dudes as you can in 60 seconds of real life time. (Think SPEEDRUNrt)

BRIDGE
As you spawn in a different place each time, there are no directions that can be given. Just follow the video to that corner and wait there for the red dudes. Perfect spot for a katana.


BREAKIN
This is the same map as 11BREAK. What you want to do it go in the hallway beside the glass room and wait around the corner, preferably with a katana.


LOBBY
This is the same map as 31LOBBY. Go to the right off the beginning and wait around the farthest corner (if at the main spawn). The red dudes will only ever come from the side you just came from. If the red dudes are not coming try stepping out and breaking the other pane of glass.


OFFICE
This is the same map as 27OFFICE. You will spawn in a different spot every time, so no use giving directions. But try to find the elevator and sit around the corner to the right. Get a katana as soon as possible.


(I know it says I dont have this achievement, but I have it preloaded)

SUPER HOT
/Can’t get enough easily
text.exe - During Endless, enter the level “Office”, grab a katana from one of the incoming enemies, facing the door from the inside hide in the top-left corner, and just start slashing all the red-guys that come in. -
Mind is Software, Bodies are Disposable, join us you can do it.