This page documents information about Hammerin' Harry. Many of the tricks demonstrated here are near impossible in real time and documented for the purposes of creating Tool-assisted Speedruns.
You can kill 2 enemies at the same time with the hammer, even when they're on opposite sides of you! You need to time your attack well to pull this off.
Crouch attacks deal 2 damage to most enemies as opposed to 1 damage. The sole exeption is the stage 3 boss in the car, who takes regular damage from any attack.
By moving to the right (or left) and attacking each 6th frame, the game will think that you stand on solid ground all the time. This allows you to walk on air, and it can be used to get off the autoscrolling boat in level 3 faster.
The movement pattern of this game is 1-2-1-2, etc. If you jump on a frame where your subpixel position ($0438) is 128, your jump will be 1/2 pixel longer.
If you are in close range of an enemy, and you perform an earthquake shatter (do a crouch attack in midair and hit the ground during it) 1 damage is dealt. This saves much time on the first boss.