Well, the thing about playing a singleton is that, no matter how far you advance one character, theres a point where you simply cannot progress any further.
This happens because as the character advances, (s)he advances at a slower and slower rate, until the player becomes too weak in comparasson to the enemies posed. This has happened in all Avernum games I try to beat with a singleton as well.
Paralasys spells don't make the situation any better either.
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Oh yeah, as for the Drake, I usually kill it by lureing it out of it's cave, then around the lower caves. All the while, I cast ice lances and slow spells on it. I make sure to clean out the lower caves of monsters before I do this too.
Slow spells were insturmantal in beating the Drake. I also found them useful when beating the big purple plant thing in Avernum 3. ( Slime caves. ) I stayed completely out of range of the thing. It couldn't move, so it never landed a hit.