Single black dragon - how far can you get?

[impy]

arena of death completed. boy, was it tough, i went through some cigarettes
First fight against great many hayterants was everything but easy. if you come close, they do critical attack. If you leave them, they lay eggs. I hid dragon behind traps, kept casting fear, few demon portals + death star.
Second fight was ok. Since Harrum only casts divine armor, i turned brontors into sheep, avoided tyrexes, and mystic egg did the job.
It now leaves gremlion, since i do not think k'tahu can be defeated.
Pretty charming still, if everything but last two bosses can be beaten with single creature
That brings the question - would it be teoretically possible to defeat k'tahu with red dragon instead, so you can heal him?