4 heroes took an epic and long struggle to take control over that encounter - loyal leader was left with 1hp (and survive few attacks with lucky defense dices) but finally loyal leader was placed in a room behind a narrow passage that was block by heroes - no monster could enter. When most of the monsters were killed heroes started to collect treasures and found a suuuuuper cooool secret room - draw "few" cards from the shop and take 1 for free. So they avoid killing corrupted leader on purpose to gather the loot.
And that's when OL played Blood Rage on corrupted leader (attack twice and be defeated) to prevent heroes from getting rich. Corrupted leader was defeated and the encounter ended.
Legal or not ?
Rules: "A corrupted leader is treated as a monster figure in its own group."
Blood Rage:"Play this card at the end of your turn and choose a monster. That monster immediately performs 2 attack actions and is then defeated".