Straight off the bat, I think you need more endurance reduction in summon demons and demon prince. Summon demons has one demon with AoE heal that he likes to spam, and the gargoyle with a resistance debuff aura. Demon prince sucks down the endurance with his two auras. You did a good job of getting the pet bonuses in there. I like your focus on recharge on hell on earth; they don't really do enough damage to enhance.
You went for a lot of global recharge bonus which always helps on dark miasma. Do you have enough to get tar patch and howling twilight recharged for maximum debuffing?
Petrifying gaze isn't the best hold, but it does stack with your dark servant's holds. This leads to my next comment. I like the demon personal attacks for the mastermind, but I would have a very hard time skipping an AoE immobilize and a single target hold at that level. The single target hold stacks with your petrifying gaze and dark servant hold. Some hard targets such as AVs and EBs can be held with enough magnitude of hold applied. Also numerous AVs are susceptible to immobilize even if other controls are heavily resisted. The black scorpion AoE immobilize will also stack with the dark servant's tenebrous tentacles.
Of the three personal attacks available to the mastermind, I like crack the whip the most.
One other observation: I see you four slotted stamina to get the set bonus from performance shifter, but an Acc/Rec in a power that uses neither is a bit of a negative to me when all your other powers are so nicely slotted except the holds 
Triumphant Defenders Forever
Psylenz FF/Psi, ArticQuark Storm/Rad, Symon BarSisyphus Bots/psn, Max VanSydow Thugs/Dk, Cyclone Symon Bots/stm, Blue Loki Ice/Cd, Widow 46526
HelinCarnate:OMG it is so terrible. I have the option to take 3 more powers but no additional slots. Boo F'ing hoo.
Any feedback...I wanted to softcap for smashing/lethal...I mostly do PVE with a desire to try to take down AV's...
Villain Plan by Mids' Villain Designer 1.90
http://www.cohplanner.com/
Click this DataLink to open the build!
Level 50 Magic Mastermind
Primary Power Set: Demon Summoning
Secondary Power Set: Dark Miasma
Power Pool: Flight
Power Pool: Presence
Power Pool: Speed
Power Pool: Leadership
Ancillary Pool: Mace Mastery
Villain Profile:
Level 1: Summon Demonlings
- (A) Sovereign Right - Accuracy/Damage/Endurance
- (3) Sovereign Right - Resistance Bonus
- (7) Blood Mandate - Accuracy/Damage/Endurance
- (7) Blood Mandate - Accuracy/Damage
- (9) Edict of the Master - Accuracy/Damage
- (9) Edict of the Master - Defense Bonus
Level 1: Twilight Grasp- (A) Touch of the Nictus - Heal/HitPoints/Regeneration/Recharge
- (11) Touch of the Nictus - Accuracy/Healing
- (11) Touch of the Nictus - Accuracy/Endurance/Recharge
- (13) Doctored Wounds - Heal/Recharge
- (13) Miracle - Heal/Recharge
- (15) Theft of Essence - Accuracy/Endurance/Recharge
Level 2: Tar Patch- (A) Pacing of the Turtle - Endurance/Recharge/Slow
- (15) Tempered Readiness - Endurance/Recharge/Slow
- (17) Impeded Swiftness - Chance of Damage(Smashing)
- (36) Recharge Reduction IO
Level 4: Lash- (A) Empty
- (46) Empty
- (46) Empty
Level 6: Enchant Demon- (A) Endurance Reduction
Level 8: Fly- (A) Blessing of the Zephyr - Knockback Reduction (4 points)
Level 10: Darkest Night- (A) Dark Watcher's Despair - To Hit Debuff/Endurance
- (33) Dark Watcher's Despair - To Hit Debuff
- (33) Dark Watcher's Despair - To Hit Debuff/Recharge/Endurance
- (48) Dark Watcher's Despair - To Hit Debuff/Recharge
Level 12: Summon Demons- (A) Sovereign Right - Accuracy/Damage
- (17) Sovereign Right - Accuracy/Damage/Endurance
- (19) Blood Mandate - Accuracy/Damage
- (19) Blood Mandate - Accuracy/Damage/Endurance
- (21) Resist Damage IO
- (21) Resist Damage IO
Level 14: Provoke- (A) Mocking Beratement - Accuracy/Recharge
- (33) Mocking Beratement - Taunt/Recharge
- (40) Mocking Beratement - Recharge
- (45) Mocking Beratement - Taunt
Level 16: Hasten- (A) Recharge Reduction
- (23) Recharge Reduction
- (25) Recharge Reduction
Level 18: Shadow Fall- (A) Steadfast Protection - Resistance/+Def 3%
- (23) Defense Buff IO
- (25) Serendipity - Defense/Endurance
- (46) Gift of the Ancients - Defense/Endurance
- (48) Luck of the Gambler - Recharge Speed
Level 20: Fearsome Stare- (A) Siphon Insight - Accuracy/ToHit Debuff
- (34) Siphon Insight - Accuracy/Recharge
- (34) Siphon Insight - ToHit Debuff/Endurance/Recharge
- (34) Siphon Insight - ToHit Debuff
- (36) Siphon Insight - Accuracy/Endurance/Recharge
- (36) Fear Duration IO
Level 22: Hell on Earth- (A) Call to Arms - Defense Bonus Aura for Pets
- (27) Expedient Reinforcement - Resist Bonus Aura for Pets
- (27) Recharge Reduction IO
- (29) Recharge Reduction IO
Level 24: Howling Twilight- (A) Recharge Reduction IO
Level 26: Summon Demon Prince- (A) Impeded Swiftness - Chance of Damage(Smashing)
- (29) Sovereign Right - Accuracy/Damage/Endurance
- (31) Blood Mandate - Accuracy/Damage/Endurance
- (31) Sovereign Right - Accuracy/Damage
- (31) Blood Mandate - Accuracy/Damage
Level 28: Maneuvers- (A) Red Fortune - Defense/Endurance
- (37) Red Fortune - Defense/Recharge
- (37) Red Fortune - Defense
- (37) Red Fortune - Defense/Endurance/Recharge
- (50) Red Fortune - Endurance/Recharge
- (50) Luck of the Gambler - Recharge Speed
Level 30: Tactics- (A) Gaussian's Synchronized Fire-Control - To Hit Buff
- (43) Gaussian's Synchronized Fire-Control - To Hit Buff/Recharge
- (43) Gaussian's Synchronized Fire-Control - To Hit Buff/Recharge/Endurance
- (43) Gaussian's Synchronized Fire-Control - Recharge/Endurance
- (45) Gaussian's Synchronized Fire-Control - To Hit Buff/Endurance
- (45) Gaussian's Synchronized Fire-Control - Chance for Build Up
Level 32: Abyssal Empowerment- (A) Endurance Reduction
Level 35: Petrifying Gaze- (A) Empty
Level 38: Dark Servant- (A) Cloud Senses - Chance for Negative Energy Damage
- (39) Siphon Insight - ToHit Debuff
- (39) Siphon Insight - Accuracy/ToHit Debuff
- (39) Siphon Insight - Accuracy/Recharge
- (40) Siphon Insight - ToHit Debuff/Endurance/Recharge
- (40) Siphon Insight - Accuracy/Endurance/Recharge
Level 41: Scorpion Shield- (A) Gift of the Ancients - Defense/Endurance
- (42) Serendipity - Defense/Endurance
- (42) Defense Buff IO
- (42) Luck of the Gambler - Recharge Speed
Level 44: Assault- (A) Endurance Reduction
Level 47: Crack Whip- (A) Empty
- (48) Empty
Level 49: Corruption- (A) Empty
- (50) Empty
------------Level 1: Brawl
- (A) Empty
Level 1: Sprint- (A) Empty
Level 2: Rest- (A) Empty
Level 1: SupremacyLevel 4: Ninja Run
Level 2: Swift
- (A) Empty
Level 2: Hurdle- (A) Empty
Level 2: Health- (A) Numina's Convalescence - +Regeneration/+Recovery
Level 2: Stamina