King of Tokyo: Halloween

Yes — there is no limit on the number of Costumes a monster can have at the same time (page 2).

No — stealing a Costume does not negate the damage; you still deal the damage you would normally deal, and you must pay the Costume's cost in energy to the monster you stole from after ending your roll with the required attack icons (page 2).

If a monster ends its rolls with at least 3 heart icons, it draws the top Evolution from its deck; hearts don’t need to be used for healing and drawing works even while in Tokyo (if you run out of Evolutions a roll of 3 hearts does nothing special) (page 4).

Evolutions are kept secret until the owner chooses to play them (which can be at any time); they come in three kinds — Temporary (discard after use), Permanent (stay in play), and Gift (stay in play but may be passed to another monster when the owner deals damage) (pages 3–4).

No — power cards that refer to ‘cards’ in the base set never apply to Evolutions (page 4).

Shuffle the Costume cards into your regular deck of cards; optionally, every player may start with one random Costume while the rest are shuffled into the deck (page 2).