Enchanter Tashan line really work? I dont think so
 

My low level enchanter gets more resists it seems when he Tashanis a mob vice when he doesn't. No hard evidence that it doesn't work but enough personal experience that I won't use it anymore for now anyway.

Without a doubt works.

Cast it on yourself, you'll see that it works just fine both duration and resist reduction amounts; what sucks is a lot of mobs are just plain resistant even with tash debuff on them. I think they eat a lot of dwarves and gain that natural magic resistance.

There was supposedly a bug earlier where mobs with the level 56 tash (tashanian) became basically immune to MR-based spells. But that has been resolved.

Haven't had any probs with any of the Tash spells, working as intended as far as I am concerned.