Exalarc, Grand Metachron

Time Dynamo - Whenever this creature attacks, you may return one of your other creatures from the battle zone to your hand. If you do, reveal a number of cards from the top of your deck equal to that creature's level. Choose a spell from among the revealed cards whose level is less than or equal to that creature's level, and put the rest on the bottom of your deck in any order. Then cast that spell for free.