Honestly, his second trait is more universally usable than his third trait. “Burn all” is is fairly lackluster by itself, we’ve all seen that before, several troops have a way to get every enemy troop burning, including Jarl and Sheggra who can do it just by matching enough gems. What is important is this is the first troop that is capable of both primary board mod with a spell (alibeit random, which can bite you hard) and invoking a storm (albiet on a trait which makes it necessary to fulfill a condition) at the same time. I’ve never been too keen on storms because you always give the enemy the first crack at the board when you use them, but Infernus breaks the mold in this regard. The storm makes it so that he can get an extra turn and full mana off red cascades after exploding, oftentimes being able to cast 2 or 3 times in a row and finish off the enemy team if he gets a kill with his spell, since the storm is summoned before the gems drop. This puts him solidly a cut above the Stryx and Guild Wars crowd as a storm user. Hes still random in both his targeting and his ability to secure extra turns and it is that which holds him back the most if you are trying to build around some kind of always-works strategy, but overall he is pretty solid, even if he does have druid-like damage (that is, if druid is ever made to deal splash damage like similar troops).
This was my first thought for him, that and rock troll/dark troll/infernus/elemaugrim. I would generally use Infernus first because I want that cascade kill to trigger the firestorm and keep my mana engine going, since Elemaugrim still misses the extra turn quite a bit.
This is similar to the second team I came up with for him… Gorgotha/Mercy/Sekhma/Infernus, Dragon Banner. It makes it easy to trigger the kill for the initial storm while keeping your turn with Sekhma and spamming out explosions while occasionally weaving in your other casts when you have alignment (and even if you don’t sometimes).
Still experimenting, but I really believe the best way to use this troop is to consider the Firestorm on kill first, then the burn. Or maybe even ignore the burn. Of course, since Fiery Death is in “common” trait spot, I wonder where that leaves him if (when?) other troops start getting it. Though maybe their spells wont also board mod, so Infernus could still be a “complete package” for this combination of effects.