Dwarf Transmuter, Halls of Steel
Not the best synergy, but a pretty good race if you want to kill The Indomitable early.
The thing about Transmuter is that I usually do alright, but I don't really feel like I'm living up to the potential. Anyway, this was pretty doable. WONAFYT spam as a substitute for LEMMISI wasn't as hot as I'd hoped, but it was ok. Elven Boots were nice. I went JJ, but I could've gone GG. Only my inventory stopped me, really - too many preps and glyphs. I just wanted to keep everything, what with the Orb of Lusory being large as it is, and Bear Mace being in the subdungeon with the bosses right next to each other.
One thing I regret a little is starting the boss too early. Using Bear Mace on The Indomitable burns through Death Protections rapidly and your knockback damage will be worthless if you're not backing it up. The slick solution would be to power level as high as possible and save glyphs for repeated Spirit Sword knockback strikes. Alternately, killing The Indomitable separately at a very low level for tons of bonus XP would work too. It wasn't going to be that hard of a run regardless.
Newer players might have trouble because Transmuter is a bit odd, and that's typical. It's really important to watch your CP gauge. Micromanagement can make a big difference. If your last fireball triggers Spirit Sword, then you get to have your cake and eat it.