I'll write a description shortly, but it's similar to eg. superflat in Minecraft. The mod removed all rocks, decoratives, water, biters, ... and sets every tile to "grass-1". Maybe I'll rename the mod to superflat. "autocleanup" means automatically clean newly generated chunks.
/cleanup -> cleans the current chunks and turns autocleanup on
/cleanup on -> turns autocleanup on
/cleanup off -> turns autocleanup off
/cleanup get -> print whether autocleanup is on
