Steadfast Talonmaster

Flying, vigilance
Steed (Whenever this creature attacks, once per turn, you may tap an untapped Knight creature you control. If you do, this creature gains all keyword abilities of the tapped creature and gets +X/+Y until end of turn, where X is the tapped creature's power
and Y is its toughness.)
Whenever Steadfast Talonmaster becomes a steed, you may gain 2 life.