A couple skins are causing my framerate to plummet

Recently I've seen a couple skins cause my framerate to drop by more than half whenever the character is on the screen. The framerate recovers as soon as they are outside the screen.

Last week it was Zombie Brand; just now it was Justicar Syndra.

My computer is a brand new 15" Macbook Pro with a Radeon Pro 460 GPU.