Barnibus, The Champion

Tap another untapped human or knight you control: Barnibus gains +1/+1 until end of turn. If this ability has been activated 3 times this turn, Barnibus gains First Strike and Vigilance until end of turn.
Barnibus can block an additional creature for all tapped human and knight creatures you control.
If you control 4 or more tapped human and knight creatures, Barnibus gains indestructible while blocking.