ToME: the Tales of Maj'Eyal

I keep hitting a wall with my disease Corruptor build when facing the Weirdling Beast. Bone Shield? Devoured. Drain/Soul Rot? 40% blight resistance. VD/Cyst Burst/Catalepsy? 100% disease immunity. Bone Spear/Grasp/Nova? Ahhahahahaha.

My skill selection works fine against every other tier 1 and 2 boss, but the Weirdling Beast is my Corruptor's kryptonite. What can I do to beat it without losing lives?

Epidemic and try later.

You could get Epidemic, which ignores disease immunity; it's a start, at least