When it deals combat damage to player, reveal that many cards from the top of your library and put a creature or land from among them onto the battlefield
It had been a while since I'd really engaged with Magic: The Gathering, but a recent booster draft with friends completely rekindled my interest
The best way to make use of this phase is with activated effects that trigger when creatures are declared as attackers, such as Asari Captain or Isshin, Two Heavens as One
Attunement fits this bill, but it combines with Replenish to bring all those discarded enchantments (you were discarding enchantments, right?) back into play in one fell swoop
Given how many decks play a handful of mana rocks and utility artifacts, its not hard for this to be swinging for four to eight damage in the early game
1 Trainer cards produced for the few winners making them some of the rarest Pokmon cards in existence