As this artifact enters, choose a creature type.
Creature spells you cast of the chosen type cost less to cast.
At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.

Commander ninjutsu (, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand or the command zone tapped and attacking.)
Whenever a Ninja you control deals combat damage to a player, reveal the top card of your library and put that card into your hand. Each opponent loses life equal to that card's mana value.

: You may return another creature you control to its owner's hand. If you do, this creature gains indestructible until end of turn.

Mutate (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Double strike
Whenever this creature mutates, it deals 4 damage to target creature or planeswalker an opponent controls and you gain 4 life.