The Dawnhart survivors welcome recruits of all shapes and sizes.

Rural Recruit

Training (Whenever this creature attacks with another creature with greater power, put a +1/+1 counter on this creature.)
When Rural Recruit enters, create a 3/1 green Boar creature token.

Innistrad: Double Feature

Innistrad: Crimson Vow

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.