Plan B allows you to convert spare cards to damage, without being an attack. This can be either a blessing (if you're stunned, or Intangible) or a curse (if you were wanting to clear that stun).
Note that this is a fairly inefficient way to convert cards to damage. Two damage for one card is fine, but since you have to pay 1+card up front before you're allowed to start making that trade, it really only breaks even after about five uses (1+6 cards for 10 damage).
Might be best in Protection or Justice, as Aggression and Leadership tend to have better access to efficient ways to put out damage. And as hinted above, could be good for Vision if you're planning on spending a lot of time in tank mode.