Although theres certainly no IEEE standard for tribal decks, Id say that at least half the creatures have to be of the creature type in question in order to consider it tribal
You can take your opponents' stuff for yourself if you deal damage with enough pirates
A Note on Ante Cards Ante cards are tutorable, but due to the way they function, they won't reap you any benefits, as confirmed by Mark Rosewater: Q : Can Spike, Tournament Grinder get ante cards
While it's important to note that Jerren is a double-faced card that can be transformed if its controller's life total is exactly thirteen, this transformation is quite difficult to trigger
If you do, each opponent loses 1 life and you gain that much life.) Whenever this creature attacks, you may return target artifact, creature, or enchantment card from your graveyard to your hand