[Edi]

The gorgon shield can help him if it gets through the MR 20 of the doom horrors, but just load up the Dom3 DB and take a look at the following guys:

Hunter of Heroes
Maker of Ruins
Eater of Gods (no kidding, especially the two latter forms with true ethereal)
Eater of Dreams
Abomination of Desolation

The Maker of Ruins and the Abomination of Desolation are pretty damned nasty and the other guys aren't exactly what you want to invite for a picnic either. Normal horrors are cute little fluffy-bunnies compared to these fellows.