KEEP
At the end of your turn all monsters take 1 damage (including you), unless you pay 1 (energy).

From Zombie 15' Kickstarter campaign:

Our Fifth Sweetener - The Horde Promo Card for King of Tokyo

If you buy this card, it means that the Zombie Horde has been released on all of the giant monsters. Yes, those zombies are gnashing and gnawing at The King's hairy ankles, and scratching at Cyber Bunny's metallic legs. (Even the Kraken will be chewed on, believe it or not! He's chewy, and tastes fishy...)

Sure, the zombies are tiny compared to the giant mons ...