Inner Flame is incredibly fun
So very very true.
Yeah, I wouldn't use it on orc wizards. Blink, enough MR to maybe resist, and invs could all mean trouble. Target the vanilla orcs, or whatever the weakest type in the band is.
Inner flame is also
fantastic as crowd control against the now more common bee vaults. Careful play can keep them walled in behind flame clouds and blowing each other up. Of course, bees are
fast, so be careful that you don't let a flamed one get adjacent to you. And even with Vehumet, and constant explosions, you can have mp conservation problems when trying to contain a large crowd this way early on. Inner flame + wand of enslavement is also
great in the early levels- especially for sending weak things on kamikaze runs against powerful uniques.
I've found inner flame hard to work against ugly things- they resist maybe 1/3 of the time, and move fast enough / have enough hp to sometimes close before exploding. Also works on undead (physical ones, like zombies and skeletal things, at least), but it can be pretty tricky to use effectively against things like skeletal warriors.
Later in the game it actually gets
better, since damage scales with monster size. It's fantastic when you get enough spell power to drop inner flames in bands of big things like trolls, ogres, death yaks, elephant, yaktaurs... The one draw back is you have to limit yourself to things with lower MR.
Inner flame detonations do not circumvent mummy curses.
Experience based off my DrFE. Fast races might be able to kite more and better exploit, and races with better int growth or fire apps might be able to overpower enemy MR better.
For added fun, stack inner flame with other thing. Sheep pack + inner flame + sticky flame = panicked baa-ing terror running and exploding in all directions (which can be weaponized- they flee
away from you, so you can get them to go
towards something else). Fireball + inner flame + giant spore = 3 explosions in one turn. XD