Looking over your list with
@Sinis .
So it seems that the plan is to get to 6 apostles, sac them, get a tutor, and go get thrumming stone?
At first I was questioning
The Cauldron of Eternity, but I see that it's to combo with the thrumming stone to put the disciples back on the bottom, and loop them with Judith for the kill. As a combo, this is naturally very glass cannon.
I also see the Grenzo + Cauldron + Ashnod's Altar + Judith kill.
Tainted Strike was a question we had earlier, but we've caught that it goes onto Judith for the kill.
So the priority of the deck would be to get the combo, protect it, and disrupt your opponents.
Interaction
For that, the first thing that we note is that your interaction is very low. You have no removal to speak of. Some amount of interaction would be good to disrupt your opponents, such as
Abrade or
Goblin Cratermaker.
Tragic Slip or
Murder for creature removal.
Damnation and
Toxic Deluge may fit well in the wrath slots.
Feed the Swarm and
Pharika's Libation are your options for enchantment removal.
Living Death is a good board wipe that fits the theme and goals of your deck as well.
I would also recommend
Imp's Mischief for fighting counterspells on the stack, possibly
Red Elemental Blast or
Pyroblast if counters are big,
Ricochet trap or
Fork effects if you want to be less narrow.
Warping Wail can help protect against wraths, while serving additional utility.
These are especially important since your combo seems to be easily disrupted by creature removal, artifact removal, or even GY removal.
Buried Ruin can help return your combo pieces, as most are centered around artifacts.
Ramp
Mox Diamond is card disadvantage for a deck that's not wanting that, and also seems difficult with 36 lands.
Mox Tantalite also seems questionable, since it's also a large card disadvantage. Even with the mass of 1 cost creatures, your demons are expensive, and 36 lands seems low.
Mind Stone is more costly on the CMC, but might provide more utility overall.
Draw
Draw seems to be focused on small numbers of big spells. While the apostles can tutor out some draw, there's only 7 draw spells in the deck, that's not bad, but I usually like to see at least 8, if not more. Possibly
Corpse Augur could have a place in the deck.
Wheel of Fate seems a little slow,
Magus of the Wheel would be preferred over it.
Promise of Power could be a good draw option as well.
Underworld Breach seems questionable on the recursion side, as you'll rapidly run out of cards in the graveyard.
Magus of the Will may be preferable to it.
Questions
Rakdos, Lord of Riots Doesn't seem to contribute much to the plan. I suppose it's a way to get big demons from the hand into play, but he seems questionable to trigger.
Blood Speaker seems to be a questionable tutor. You don't really want the demons in your hand.
Demonic Tutor seems more flexible to get your other combo pieces.
Angrath, the Flame-Chained seems questionable - he doesn't do very much for 5 mana. If you're looking for hand disruption, perhaps
Mindslicer is more where you want to be, though
Sire of Insanity seems to already hit the spot.
Lands
Cabal Stronghold seems questionable, as you only have 8 basic swamps.
Myriad Landscape could be low opportunity cost ramp.