Thunderblade Charge

Oracle Text

Thunderblade Charge deals 3 damage to any target.

Whenever one or more creatures you control deal combat damage to a player, if Thunderblade Charge is in your graveyard, you may pay 2RRR. If you do, you may cast it without paying its mana cost.

Card Rulings

5/1/2007 When the ability triggers, first you choose whether to pay . If you paid, then you choose whether to cast the spell.
5/1/2007 Thunderblade Charge triggers only once per combat damage step no matter how many of your creatures deal combat damage to a player, how much damage is dealt, or who that player is. (It might be you if the combat damage is redirected.) However, the ability could trigger twice in the same turn if there are multiple combat damage steps due to first strike or double strike.