The griffin is immortal.

Does anyone know what’s needed to unlock the green key master with liches? I’ve already done everything else, only this remains. For those interested, here’s how I dealt with the knight who wouldn’t catch up in the dungeon. I lured him out with a level 6 unit during the Week of Equilibrium (which is important!) and defeated him with three low-tier units (1500 archers, 900 zombies, 340 ghosts), using sword walls and fists.