Bugfixing: farm edition

Created by: ComicIronic

Removes a misspelling in the code that was defining an extra object. Fixes #4075 (closed), mobs only retaliate if alive. Fixes #4059 (closed), makes sure sprites are only generated after being set. Also removes unnecessary \improper. Fixes #3817 (closed), mask layer wasn't being updated, see the issue for details. Does a little bit for #3699 (closed), null rods now check range.