Keyboard[]
customizable
wasd = move
q,e = turn
TAB = Map (can be turned off)
ESC = menu
Mouse[]
completely mousable
RMB+LMB required (except in tablet mode found in the game options)
Additional Info[]
Windowed works (no resolutions below 1280)
Subtitles
OSK works
Enable Viacam headmouse works
natively no gamepad, XPadder might work
Important[]
Just a little warning:
While Grimrock has a control scheme that helps mouse-only gamers, it is still a game that demands quick actions. Casting spells is specially hard as you have to dial in the required symbols which becomes almost impossible in the heat of a fight.
There are puzzles with extremely (!) thight timeframes that cannot be solved using a headmouse along with the on-screen keyboard.
Here’s a link that contains info on how to slow down The Legend of Grimrock in order to gain longer reaction times. I can’t tell if it helps to completely play through the game but it does enough to let you win against quick opponents.