This is an amazing card that I didn't know about. It's a repeatable Unsummon except that it's colourless. Imagine what a Momir Vig, Simic Visionary or Animar, Soul of the Elements EDH could do with this. How about 60-cards based around ETB triggers and Cloudstone Curio? This card can easily air-juggle opponents' creatures and cause them to never leave turn 5 or 6, forcing them to constantly replay the same turn over and over again until you finally kill them with your tiny creatures. The one flaw that I can see with this card is that it would lose very hard to token decks, since you probably won't have the mana to keep the masses in check.
Pros: Repeatable colourless Unsummon
Cons: Requires mana