Hopeful Initiate

Training (Whenever this creature attacks with another creature with greater power, put a +1/+1 counter on this creature.)
{2}{W}, Remove two +1/+1 counters from among creatures you control: Destroy target artifact or enchantment.

Magic Online Promos

Innistrad Remastered

Training
{2}{W}, Remove two +1/+1 counters from among creatures you control: Destroy target artifact or enchantment.

Innistrad: Crimson Vow Promos

Innistrad: Double Feature

A creature's training ability triggers only when both that creature and a creature with greater power are declared as attackers. Increasing a creature's power after attackers are declared won't cause a training ability to trigger.

Once a creature's training ability has triggered, destroying the other attacking creature or reducing its power won't stop the creature with training from getting a +1/+1 counter.