Simple RAW 3

[Erys]

Q18: A vampire regains health at the beginning of its turn unless it took radiant damage in the last round after its last turn. Spirit Guardians deals radiant damage at the beginning of the enemy's turn. If Spirit Guardians triggers for the first time against a vampire, does it regain health that round?

A18: Assuming the spell was cast while the vampire was within 15', thus mitigating the 'entered' effect of the spell- I think falls in DM territory. I don't see a concrete RAW answer from my searches.

If it was me, the vamp would heal half what it usually does for that round. YMMV

Two questions:

Q19

Can someone explain how animals' attack stats are figured out? It doesn't seem to be consistent. For example, The brown bear has a +5 to hit with its bite and claws, but its strength modifier is +4. It has a +2 proficiency based on its CR of 1, so why is it not +6? A Camel has a +2 proficiency bonus, but only has a +3 strength mod and yet still has a +5 to hit. What am I missing? Is it just a typo that never got caught?

Q20

When you Wild Shape, do you use your own proficiency bonus or the animal's? You get the creature's statistics, but you keep your own class and racial features. Is your proficiency bonus a class feature, or am I stuck with whatever the animal has for a proficiency bonus?

A19: Probably a typo. I don't see any errata on it though.

A20: You get yours for saves and skills you know, use its for things it knows that you don't (like biting and clawing people). Cite

Q21
If I have extra attack and kill a creature with my first attack, can I use the rest of my movement to move to another creature and hit that one?

A21: Yes. (PHB 190)