Sharn, Guileful Rogue

When Sharn, Guileful Rogue attacks, you
gain +2/+3 and flip a coin. if you succeed,
you may select an opponents target creature
to block, then roll a D20.
0-9 - No effect.
10-18 - Gain Double Strike.
19-20 - Sharn finds the creature's back, gaining deathtouch, Indestructable, Double Strike and doubles her power.