Oh, the last Mage. Yeah, he's a bugger.
The spell he casts actually shields the obilisk and prevents you from using it. And yes, the "shock ball" the shield casts out are deadly. A friend of mine that cheats constantly (no challenge there, imo), even found out they kill people though the "invincible" cheat code
Personally, I love that touch. Means pure cheaters are screwed at that stage until the learn to actually play the game
Slow spells and weapons that petrify/freeze are nice to take against boss-casters. Slow spells sometimes make them "fumble" spells, and petrifying/freezing stops them cold
~Jessy