I treaded carefully today, as I always do with the Rat. I used my health-based resources to fight Bjorn, then used a quicksilver to land some corrosion on Bleaty and then unloaded all my mana-based resources on top of him. Thanks to that lovely subdungeon I could afford to purchase everything I wanted, so it wasn't too bad. Still had two mana potions left over when I was done. Planned to join Taurog and use GG desecration and Pactmaker Consensus to go for Unstoppable Fury once I ran out of spellcasting resources, but that wasn't necessary.
I was disappointed that I didn't find the Balanced Dagger until it was too late to put it to much use, but being positioned off in the corner like that it wasn't exactly unexpected.