Well the henchman themselves would be nerfed to hell. 
Not sure about the Cyst. What do you do with it? Plant it like /Traps and let it spawn for you?
It might be better to go with 3 Dark Extraction types for the first tier, 2 Nova at the second, and 1 Dwarf at the end. They would still be much weaker than the actually AT though and I have no clue what you would do for the upgrades.
"Mastermind Pets operate...differently, and aren't as easily fixed. Especially the Bruiser. I want to take him out behind the woodshed and pull an "old yeller" on him at times." - Castle
I guess I should have mentioned that "Kheldian Summoning" was just an idea and the pet hierarchy was barely thrown together. I myself am only just starting to seriously think about it.
I figure the Cyst would be like Gang War or something: the Cyst itself would be like a Phantasm but with no powers other than to summon Unbound Nicti, and could be shielded, healed, and destroyed. The Unbound Nicti would have to be underlings, I guess? They'd spawn in numbers relative to the number of enemies in the Cyst's vicinity.
Storm Summoning is great because it makes you better than everyone else in the game. - Camma
Knockback is mitigation. It won't be removed just because meleers ***** and moan. - Chaos Creator
I think 3 Unbound Nicti, 2 Novas, and 1 Dwarf would make an awesome set of pets.
Have the Nova start off with the one single-target attack, then give them the high damage single target and the cone on the first upgrade, then give them the AoE and maybe another attack on their third upgrade.
Same thing for the Dwarves. But put their Self Heal in the second tier and have it auto-fire at 1/2 health.
-Rachel-
This idea came out of an unproductive thread elsewhere on the board, and I was wondering if it would be game-breaking to actually introduce such a thing: a Mastermind with Nictus primary and..."Umbral Domination" or something secondary.
The pets would be 3 Dark Novas, 2 Black Dwarves, and maybe a Cyst Crystal as the top-tier. Secondary would consist of the Warshade buff/debuff/control powers and such.
Any downsides to this?
Storm Summoning is great because it makes you better than everyone else in the game. - Camma
Knockback is mitigation. It won't be removed just because meleers ***** and moan. - Chaos Creator