I am trying to understand what is the skill tree Killer Vegan and how does it work, unfortunately the two main wikis for Dungeon of Dredmor do not describe it.
Can you give me some hints?
There are 5 skills under Killer Vegan. The Dredmor wiki has been updated with detailed information on these skills and debuffs.
If you have Killer Vegan as a skill tree, and you injure an animal, you'll get a debuff of -5 to most of your primary skills, plus -5 health and mana regen for 200 turns. This debuff stacks 3 times. There's also a debuff for eating non-Vegan food, and another (more minor) debuff if you have Clean Living.