Great Princess Regna Gravnoy. She's, like, not an Infernal Master but... almost? She's a "Master Infernalist," so like a Journeyman Warcaster/Lesser Warlock. Can only summon lights/lesser Horrors. Can also just be used as a caster.
Valin Hauke, The Fallen Knight is a large based solo. Guess he has a horsey! Pretty powerful, they've been testing Long Shadows at 5", but might change it to 3".Long Shadows reduces the range of enemy attacks. His power is also magical (its magic is NOT powered by friendship).
The Wretch is a solo, FA3. If you're in its command range you're -2 to damage roles (5CMD at the moment). Kind of scary.
Umbral Guardian, FA3 solo. Has an ability called Shadow Guardian which allows them to NOT be deployed at start. Rather, you can bring them in if an ally is going to be hit by a ranged attack. Its a "shield guard from off the table."
Infernal Gate is a structure. It collects souls, and if it can't get them? It generates them. It can bring soul-less infantry. Has a Range 12, AOE 4, POW 14 attack, and is boostable. Can also spend Essence on Knowledge of the Damned to reroll.
Mordecai, Master of Arms. He's a character the devs are watching because he's quite powerful, support-wise.
Kezia Brand, the Screaming Night. Combat solo. Very high mobility due to Parry, Pathfinder, Stealth, Acrobatics, and Run & Gun.
Not going to bother with the Theme Forces, sorry folks. I am told Hearts of Darkness Theme Force has been removed from the CID. Its a "hypothetical"/"what if" thematic theme force for Crucible, Cygnar, or Khador armies. They are basically corrupted forces that went over to the Infernals. I suppose Protectorate, Convergence, and Retribution are too divinely focused or inhuman...