The theory behind room resetting: Some rooms upon restarting move the starting position of your character which will either let you complete the room faster or slower. However the game doesn't let you restart from the moment you gain control over your character, it's delayed by a few frames, so even though in a room such as slaughter-3 you are moved just a tiny bit forward you will be losing time. That's also assuming you make a frame perfect reset. Realistically you will not perform them so you will be further losing time. Here's a technique on how to properly quick restart, hold down a dedicated roll button before you restart the room (or hold down 's' and 'd' if you're crouch rolling), this will cause your character to roll on the very first frame upon restarting the room. As for the restarting itself, you can either mash the restart button or try to time it with a single press.

Here's the list of rooms you save time by restarting (not including the time loss that may come from a slower strat) These times aren't perfect, expect them to be wrong by ~0,1s. If you are confused by which room is which use this sheet for reference.

Factory-3 0,3s Hotel-6 0,6s Club-Entry 0,1s Club-4 0,7s Mansion-2 0,05s You can restart the level in the section before you break glass and go down to V, I made sure to this properly, so even though the time save is small, if you are able to restart within ~3 frames, it saves time, though I wouldn't recommend going for that. Mansion-3 0,4s Reply skip: You have to wait 0,56s before the game gives you control over your character if you perform replay skip, restarting the level lets you shave off 5 frames of the total time. Kissyface: Upon picking up the katana you are able to restart the level, this saves 3,4s. Moto Chase: Video showing all of the moto chase restarts In all of these restarts the disk on the bottom right corner has to appear before you can restart. The first restart happens once you kill all of the enemies in the 4th wave of enemies. The second restart happens when all of the cones are off the screen or toppled. The third restart happens once you kill all of the enemies in the second wave after the cones. The fourth restart happens once you kill all of the enemies in the second waver after the third restart. The fifth restart happens at the last wave of enemies (so four waves after the fourth restart) you have to both kill all of the enemies and all cars have to go off-screen. The sixth (optional) restart happens when after you kill V, you have to wait longer than usual for the disk to appear. video of this happening. Even though the no-restart version of the heli fight can end up being faster, it's upto RNG if you save/lose time, depending on how quickly V starts shooting. In 50% of cases you can save upto a second, and in the other 50% you can lose upto a second. This is a rough estimate. Don't bother with the no-restart version of heli fight unless you get to sub-17 or so, due to the sheer difficulty of this strat. Chinatown-8 0,2s Dragon-3 0,5s Dragon-4 0,1s Slaughter-5 0,05s Same as Mansion-2, you can gain some time by doing a frame perfect restart, but you have ~3 frames of leeway. Slaughter-7 0,35s

In bunker 1 you are able to restart the room before the elevator opens which causes the doors to open faster. Bunker1-2 0,4s Bunker1-3 0,3s Bunker1-4 0,5s And so on (I can't be arsed to time each one, but they all save roughly the same amount of time).