BREEDING: Rats are nothing but not prolific. Each full experience bar becomes a new rat subject.
LOYALTY: Self-sacraficing rat subjects will hurl themselves in the way of danger. Lose a level and regenerate if you die with at least 1 rat subject.
AUSTERITY: All items are large, from a rat's perspective.
Rat Monarch gains 1 Level for every 40+15 conversion points.
My opinion:
1. The juxtaposition (XP does something else and Conversion level you up) is intriguing, although I'm still trying to wrap my mind fully around this. I guess, XP management is so engrained in my thinking after hundreds of DD runs that it's hard to even think about it right! It's new and fresh and out-of-the-box, though I don't fully get what's the benefit (other than, challenging the players' thinking).
2. I absolutely love the Austerity drawback! I mean, assuming that the class will be balanced in the end to make up for this hindrance. I really like how your "standard issue" potion kit suddenly takes up 2/3 of your inventory! Now that is a change in thinking (and challenge) that I find easy to wrap my mind around.
3. Something has been bugging me about the class. It's that emotionally I find the idea of: i) very limited leveling potential; and ii) permanent, irrevocable level penalty; a bit disappointing. I don't want to say that it's weak (I haven't done nearly enough testing to say anything like that), it's just that it doesn't feel very rewarding as a player to scrape everything together, to buy a level-up, and then lose it back (basically irrevocably) once the regeneration is triggered.
Thought Experiment
I don't intend to go anywhere with this. Just to create a mental anchor that serves to "bridge" what the Rat Monarch does, in a different, hypothetical class that is easier to understand for me, i.e. without the juxtaposition.
- level normally
- gain 1 Rat Subject for every 40+15 conversion points
- regenerate fully (and lose 1 level and 1 rat subject) if you have at least 1 rat subject and would die; reset XP bar to proportionally where you were in your bar, and reduce XP requirements to the requirements of your new (lower) level
- and of course AUSTERITY!!! (I love this

Anyway. Thoughts? Experiences? Please share!