The 2 things I have learned about my demons that have drastically altered my slotting is.
1.Ember Demons heals do not benefit from the Blood Mandates End reduction. He spams them a lot so if you do not slot End reduction in them he is sucking air halfway through the fight.
2 Demon Princes Slow powers including Aura also do not benefit from Blood Mandates End reduction so when he start chucking shivers and block out left and right he also starts sucking wind unless you slot with generic End IO
So what I did.
Villain Plan by Mids' Villain Designer 1.81
http://www.cohplanner.com/
Click this DataLink to open the build!
Level 50 Magic Mastermind
Primary Power Set: Demon Summoning
Secondary Power Set: Storm Summoning
Power Pool: Speed
Power Pool: Fitness
Power Pool: Leadership
Ancillary Pool: Leviathan Mastery
Villain Profile:
Level 1: Summon Demonlings -- BldM'dt-Acc/Dmg(A), BldM'dt-Dmg/EndRdx(3), BldM'dt-Acc/Dmg/EndRdx(3), BldM'dt-Dmg(5), EdctM'r-PetDef(5), S'bndAl-Build%(31)
Level 1: Gale -- Acc-I(A), Acc-I(9)
Level 2: O2 Boost -- Dct'dW-Heal/EndRdx(A), Dct'dW-EndRdx/Rchg(7), Dct'dW-Heal/Rchg(7), Dct'dW-Heal/EndRdx/Rchg(11), Dct'dW-Heal(11)
Level 4: Snow Storm -- EndRdx-I(A), EndRdx-I(34)
Level 6: Enchant Demon -- EndRdx-I(A)
Level 8: Hasten -- RechRdx-I(A), RechRdx-I(9)
Level 10: Hurdle -- Jump-I(A)
Level 12: Summon Demons -- BldM'dt-Acc/Dmg(A), BldM'dt-Dmg/EndRdx(13), BldM'dt-Acc/Dmg/EndRdx(13), BldM'dt-Dmg(15), HO:Golgi(15), HO:Golgi(31)
Level 14: Super Speed -- Run-I(A)
Level 16: Freezing Rain -- Acc-I(A), RechRdx-I(17), RechRdx-I(17), ImpSwft-Dam%(19), LdyGrey-%Dam(19), Achilles-ResDeb%(31)
Level 18: Health -- Mrcl-Rcvry+(A), Numna-Regen/Rcvry+(48)
Level 20: Stamina -- EndMod-I(A), EndMod-I(21), EndMod-I(21)
Level 22: Hurricane -- DarkWD-Rchg/EndRdx(A), DarkWD-ToHitDeb(23), DarkWD-ToHitdeb/Rchg/EndRdx(23), DarkWD-ToHitDeb/EndRdx(34)
Level 24: Hell on Earth -- ExRmnt-Acc/Rchg(A), ExRmnt-Acc/Dmg(25), ExRmnt-Dmg/EndRdx(25), ExRmnt-Acc/Dmg/Rchg(33), ExRmnt-EndRdx/Dmg/Rchg(33), ExRmnt-+Res(Pets)(34)
Level 26: Summon Demon Prince -- BldM'dt-Acc/Dmg/EndRdx(A), BldM'dt-Acc/Dmg(27), BldM'dt-Dmg/EndRdx(27), BldM'dt-Dmg(29), SvgnRt-PetResDam(29), EndRdx-I(40)
Level 28: Steamy Mist -- RedFtn-Def/EndRdx(A), RedFtn-Def/Rchg(33), RedFtn-EndRdx/Rchg(37), RedFtn-Def/EndRdx/Rchg(43), RedFtn-Def(46), RedFtn-EndRdx(46)
Level 30: Maneuvers -- RedFtn-Def/EndRdx(A), RedFtn-Def/Rchg(43), RedFtn-EndRdx/Rchg(48), RedFtn-Def/EndRdx/Rchg(48), RedFtn-Def(50), RedFtn-EndRdx(50)
Level 32: Abyssal Empowerment -- EndRdx-I(A)
Level 35: Tornado -- HO:Nucle(A), C'Arms-Acc/Dmg(36), C'Arms-Acc/Dmg/Rchg(36), C'Arms-EndRdx/Dmg/Rchg(36), C'Arms-+Def(Pets)(37), Achilles-ResDeb%(37)
Level 38: Lightning Storm -- Dev'n-Acc/Dmg(A), Dev'n-Dmg/EndRdx(39), Dev'n-Dmg/Rchg(39), Dev'n-Acc/Dmg/Rchg(39), Dev'n-Acc/Dmg/EndRdx/Rchg(40), Dev'n-Hold%(40)
Level 41: School of Sharks -- Posi-Acc/Dmg(A), Posi-Dmg/Rchg(42), Posi-Dmg/Rng(42), Posi-Acc/Dmg/EndRdx(42), Posi-Dam%(43)
Level 44: Shark Skin -- TtmC'tng-ResDam/EndRdx(A), TtmC'tng-ResDam(45), S'fstPrt-ResDam/EndRdx(45), S'fstPrt-ResDam/Def+(45), S'fstPrt-ResKB(46)
Level 47: Assault -- EndRdx-I(A), EndRdx-I(50)
Level 49: Vengeance -- LkGmblr-Rchg+(A)
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Level 1: Brawl -- Empty(A)
Level 1: Sprint -- Empty(A)
Level 2: Rest -- Empty(A)
Level 1: Supremacy
Level 6: Ninja Run
I put a full set of Expedient in Hell on Earth because it gives nice set bonuses plus +10% resist aura and enough hit, dam and recharge to make the little guys useful. I also put the Call To arms in Tornado for the global recharge and 5% Def. If you dont have storm secondary you can go 4 Expedient 2 call to arms in Hell on earth.
Big surprise for me: Demon prince's powers ALL have a slow. Slot the chance-for-damage slow proc and watch the numbers pile up.
Full disclosure: If you buy a level 30 crafted IO of that, I may get some money from you. 
I looked around the forum a bit and found nothing to help understand how to slot my demon pets.
Working 7 days a week, 10 hours a day now so instead of more forum searching I am just gonna ask for some help so I can use my tiny free time playing.
If some of you knowledgable folks wouldn't mind posting a clue about how slotted out your demons and Hell on Earth I would be eternally gratefull.
4 months of these hours and no end in sight has this old guy brain dead. :-)
Thank you.