If an opponent casts a creature spell with flash while the token is attacking or blocking, the token is removed from combat because it stops being a creature
The first is Ainok Strike Leader, a bear who when it or your commander attack it creates a 1/1 goblin attacking each opponent
Artifact - Book Sorcerer Class (Gain the next level as a sorcery to add its ability.) When this Class enters, draw two cards, then discard two cards
The artifact requires a pretty high cost to get the chain started, though - four mana (or three and two life) to cast, then two mana (or one and two life), a tapped card and a sacrificed creature to set its ability in motion
Read on for my in-depth impressions of this exciting cross-over, including an HD gallery and where you can find these cards to build your own collection
Playing an item early on means you might get to use it a few times, making it very valuable