I'm a fan of Mogis decks, and always happy to read one over to steal ideas and make suggestions.
Necroskitter IS cool, but works better if you can regularly ensure opposing critters have -1/-1 counters. Outside of
Everlasting Torment, I didn't see anything else.
Black Sun's Zenith,
Carnifex Demon,
Corrosive Mentor,
Fevered Convulsions,
Harbinger of Night,
Liliana's Influence,
Midnight Banshee,
Kulrath Knight,
Puncture Blast,
Soul-Scar Mage,
Soul Snuffers,
The Scorpion God, and
Stigma Lasher might help here.
Stigma Lasher is another life-prevention option, as well.
Braid of Fire is a fun card in the right deck. I say that, because all the mana has to be used during the Upkeep step, and your deck has few options.
Fault Line,
Comet Storm, and
Magmaquake immediately spring to mind.
Blast Zone, maybe, as a mana sink?
There are a few fine pingers to consider adding:
Last Laugh,
Pestilence, and
Pyrohemia. Your commander ensures that none of these ever go away. I do like how
Mayhem Devil plays nice with your various self-inflicted and forced sac outlets.
Fanatic of Mogis is more than just a pinger, but with all your red devotion, it IS thematic perfection.
Heartless Hidetsugu approves of your damage doublers. So does
Glacial Chasm.
Overall, your deck seems aimed more at dueling than at multiple opponents. There is nothing wrong with this, but in the face of many players, it may
backfire - especially as you are losing the life gain AND having most damage doubled against yourself.
Also, I don't see any means to blow up artifacts or lands, two of red's strengths (you kill creatures and planeswalkers, though).
Fulminator Mage has been printed into affordability.
Ghost Quarter and
Torch Fiend/
Reckless Reveler help, as well.
Feed the Swarm provides a means to
zap an enchantment. You don't need to run these types of cards, but might consider it.
Smash to Smithereens and
Builder's Bane play nice with your damage doubling.
Tutoring can be strong, but sometimes naked draw is better. Black has numerous options here, but red can wheel and has
Magus of the Wheel, another self-sacrificer.
Now I want to build a deck around -1/-1 counters.
The Scorpion God or Hapatra, most likely.