Nereus has been fighting his way through this particular dungeon until his arms feel fit to fall off, until he's shaking. He got lucky with this pocket dimension, and no one else seems to know about it yet.
But dungeons are usually handled by teams, if not armies, and Nereus is one person - even if his most powerful artifact sometimes puts a lie to that.
He spins in his clones, healing himself, then starts cutting his way more narrowly through the mob of crystalline plant monsters, trying to get to a ledge he can rest on for a time.