Passive Investigation: Could replace Passive Perception?

A vampire can automatically hit a grappled target, that condition excludes an attack roll?

Can I use my second action from Action Surge for a ready action?

Does Poison remains potent until delivered through a wound?

if I cast a bonus action spell can I then cast Shield as a reaction?

What would happen to an undead if a hero blocked it’s connection to the negative plane?

When something lets you cast something at will, do you cast it as an action or is it free?