I spent ages arranging the kegs along the corridors only for Nasty to run away and regenerate as soon as he saw them.
So instead, I put them all in the caves and the crystal room, and actually carried them towards him, and then dropped them (right against the darker wall,) as he came for me. You can get two together sometimes, but no more. Retreated, blew the kegs and ran back for more as he kept coming forwards.
Crucial spells/ potions; haste and invisibility.
I blew myself up more than once!
