Gamora's Sword is an interesting card. Three cost Upgrades must be considered carefully, especially Upgrades that trigger off other actions.
Compared to simpy playing Uppercut, you have to play five Attack Events to break even. Compared to Decisive Blow you might have to play seven! If you are early in the game and you have a large number of attack events, get it down when you can! Once the mid game hits and you have your resource generators down, it may be time to be thoughtful and considering out many times you will trigger Gamora's Sword.
I rate this card a B: A good card that requires building around (lots of Attack events) but may conflict with other card plays