Shockwave

Shockwave is a 2-Energy Ironclad skill that applies 3 Weak and 3 Vulnerable to all enemies and then Exhausts (5 of each upgraded). Three stacks of Vulnerable means three turns where all your attacks deal 50% more damage; three stacks of Weak means three turns where all enemy attacks deal 25% less damage. Applied to all enemies simultaneously, this is one of the strongest single-turn debuffs in the game.

Even at 2 Energy, Shockwave often pays for itself within 2-3 turns in multi-enemy encounters by reducing incoming damage and amplifying your attacks. Upgraded to 5 stacks each, the window of effect becomes very long. The Exhaust means it's a one-per-combat play, so timing matters. Best used before a burst turn or when facing groups that will attack multiple times.