Supports non-instant spell skills. This is a Support Gem. It does not grant a bonus to your character, but to skills in sockets connected to it.

Can spells have culling strike?

Your Spells have Culling StrikeA heart can be stabbed by thoughts, If your mind is sharp enough. leaders until the others leapt to join his cause.

Does culling strike work on bosses?

Culling strike does work on rares and bosses. It works on everything.