Trolls against Infernals?

Actually, the JJrH Runeshapers list plays very well into Infernals. Arcane Vortex on Mulg can ruin Agathon or Zaateroth's day, Zaat can't abuse Black Spot because the unit sizes are so small, two 10" bubbles of no soul collection stops stuff from getting out of hand, Runeshapers absolutely shred horrors, and everything in the list is accurate so you're not worried about Zaat's feat.

I've yet to play into Omodamos or Flames in the Darkness with it, so I can't speak to those matchups.

I have limited experience against them, but in my couple of games the strategy of chewing through all of the marked souls was a non-option. Too many of them, played too far back, with too much defensive tech. It may be their weakness, but they know it, and it's just too easy for them to keep a few safe.

Dhunian Archons are fantastic anyways, and bonus points against Infernals.

She can hand out minus 4 defance(deafen and calamity) to one model(if opponent know how to position), and -2 armour in hermit aura + -2 on calamity target. of course hermit can telemetry and basher can Icy Breath,but basher will just die, and it still will mostly affect one model. And decceleration from Ragna works against Runeshapers magic attacks. The problem is not bout killing one heavy with calamity a turn. It's rather easy. It's more bout treading down in value and with every unit of shapers down we kinda loose it. Need to try to play that match up, but currently why pGrissel is my main list, trying some off lists to play it better.

Omodamos isn't that great a brick. His heavies are Def 11, Arm 21 with the boxes of a light Warjack. Killing seven of them is only about equivalent to killing five heavy Warbeasts or Warjacks, by and large. If you struggle against them I shudder to think how you go into the likes of Grymkin or Skorne.

I'm not a Troll player, my own experience against Infernals has mostly been that if you have a better threat range than them (which is usually relatively easy) you can control the game, smash a critical mass of their relatively squishy heavies on an alpha strike, and ride things out from there. Doomshaper2 seems like a reasonable pick if you want to replicate that in Trolls? And I've seen the Grissel1 Runeshaper list table Infernals a few times now, though as a spectator I have to leave it to those who actually play the list to explain how that works. It generally seems to me that the Runeshapers are content just trade pieces all game and eventually it reaches the point where the Dhunian Archons are just getting too efficient and the Infernals player runs out of models.

Oh, don't get me wrong. Omodamos is a solid Master, and Infernals are always tricky for new players to handle. But seven Horrors with Unyielding and Deceleration honestly hovers somewhere around the middle for bricks, not the top, and I would say he gets that high because his hit points are dispersed across more models (which is inherently more difficult to bring force to bear against) than because his stats are good. Five or six heavies is a lot, you're right, but it's also arguably about the norm for most "brick"-type lists. A Grymkin Dark Menagerie list will be in that realm, for example, and outside of Hordes you get lists like Karchev running a great deal more. Frankly, I'm more worried about a Borka2 brick than an Omodamos one, though sadly Valin Hauke means that I can't see Borka having a good time into Infernals himself.

I'm not an Infernals player, just someone who honestly quite enjoys playing against them. They're a fun puzzle to unpick. If you're having trouble against Omodamos, another recommendation I can think of is to try and snipe out some Cultists. He might be able to protect his Marked Souls, but Omodamos spends a lot of Essence quite selfishly and relies on his cultists to refuel. If your opponent is bringing Regna then by Turn 3 he'll have often killed 5-6 Cultists himself. If you can then kill, say, three Cultists yourself in that time, he'll be in a position where keeping his Horrors fuelled becomes pretty hard, which in turn makes Dhunian Archons more effective because two of them will basically shut off a heavy's entire activation each round. Surviving to that point is the trick, of course, since he should get 1-2 turns of having a large number of fully loaded horrors to jam down your throat, but the efficiency does wane as the game drags on.