Hey, awesome radical update on the Rat! So just for the record, the version we're now talking about is:
REGAL HYGIENE: Rat bites corrode enemies. Gains 1 stack of Corrosive Strike per level.
REGAL PERKS: Sensitive whiskers detect deals. All shops are scouted. Buying an item regenerates 50% Health and Mana (may overheal).
REGAL SIZE: Rats are the correct size: small. Lower maximum Health and Mana, all items are large.
Rat Monarch gains +1 Corrosive Strike for every 80 conversion points.
Notes: "lower maximum health and mana" means a per-level 8 Health (-2 health per level) and a 8 base Mana pool (-2 mana). Although not mentioned, base damage is significantly reduced, to 1 per level.
EDIT: Ok, I took the Monarch for a couple of spins. So far I like it very much! I agree that CYDSTEPP is brutal on the rat, L1 bosskills or any L1 kills are just plain simple with that. I guess difficulty starts where you need to kill several powreful monsters. I still think melee should be doable using maxed resists, though.
I'm a bit torn because I liked the old Rat a bit (I liked the idea, and I thought it could go somewhere fresh, even though it was not very much balanced). I think the new Rat is much more "rich", in terms of its abilities meshing together nicely, still doing things nobody else can. I feel instinctively that it's a more balanced, less one-trick-pony class, I do miss a bit the old version (or, more accurately, what the old version could have become).
So far what seems to work nicely is boost Corrosion; poke monsters via resists/dp/overheal; finish them using spells. I kind of feel that Binlor and Mystera will be prime deities, though I can see an argument for JJ's bar boosts offsetting the penalties. Popcorn is unmunchable via melee in one hit, so slowing stuff is generally only useful if you blast them. Flames boon is largely inconsequential. PISORF seems a bit lackluster due to low base damage, but knockback might be a powerful melee solution. All in all, I think this new rat is more skewed towards a more balanced, less caster-only approach, probably more viable in melee and as a hybrid.