Toxrill, the Corrosive, has the capacity to remove all opponents' creatures but it's fairly situational
Their arms have either worn away or been deliberately removed and they now paint with two brushes that are attached to them, using blood from their own veins
You can discard a card to give it Lifelink, and 'Whenever one or more cards leave your graveyard, put a +1/+1 counter on target Creature you control.' The College of Lorehold is all about cards leaving your graveyard, from casting spells with flashback to exiling cards to pay for Delve costs
You don't have to choose a target for the reflexive triggered ability created by Lockjaw's last ability, but if you do, and that target is illegal as that ability tries to resolve, it won't resolve and none of its effects will happen
The answer is that even numbers feel more structured and odd numbers feel more natural