Bigsby, Master Swordsman

At the beginning of your end step, roll a D20:
1 - 7 - Bigsby is a fraud, sacrifice him.
8 - 16 - No one has noticed, gain +2/+2.
17 - 20 - Everyone is fooled, gain +10/+10.

{t} Bigsby overcomes all odds and protects
target player. Destroy all attacking creatures
and sacrifice Bigsby.