Transmuters are weird. They're incredibly tedious to play as, can curb stomp most of the normal and hard dungeons but tend to run out of gas quickly on most of the (true) vicious dungeons, and have terrible synergy with every deity except for Glowing Guardian. (Taurog hates them more than anyone else because they are constantly casting spells; Mystera hates them because they never use MP; Tikki Tooki hates them because they like to get in slug fests with high level enemies and ignore weak ones; even Binlor hates them, because most of his boons are worthless to them and the two that might be useful tend to cost too many walls. Dracul is meh, since lifesteal and the extra resist aren't worth it unless you're primarily fighting magical enemies, and the extra MP can't be regenerated so it's of limited use. But they are great at taking out high level bruisers, and are fine with leaving alone weak enemies, so Glowing Guardian is pretty much a perfect fit.)
But spend enough time scumming for a
Rock Heart and they are
nigh invulnerable.
In unrelated news, I'm not impressed with having the witch's potions in shops - they're just of so limited utility that 9 times out of 10 I'd rather be able to purchase another health or mana potion instead (especially since you'll rarely have a situation where you need both effects and only those two effects). As preparations they're just a little something extra, but now they're crowding out more useful items from shops.
Conversely, the Battlemage Ring is probably also overpowered, though I haven't tried it out much yet. Twice as powerful as Mystera's Flames boon but with no penalty? A big offense bonus that scales as you level, but is just as effective at level 10 whether you bought it at level 1 or a level 10? Not to mention, as a level 10 character against a level 10 enemy, it will give you just as much extra power as the nerfed Flame Heart, only it reaches full power right from the start rather than after your 20th fireball. I kind of like the idea of having it make fireballs more expensive - like, +1 or +2 MP cost - which is still more damage-per-mana than a normal fireball, but its immense power would be balanced out by less flexibility.