MalZenith

I'd take out Kragma Butcher and a couple Kragma Warcallers for some of the earlier drop minotaurs, such as Gnarled Scarhide and Deathbellow Raider. They won't last too long, but Gnarled Scarhide has lategame utility and Deathbellow Raider has decent survivability. You have a plearth of 3-drops in the deck, so much that you'll have too much to do on Turns 3-5, but not enough good threats to play once you've exhausted your hand. Instead of Fearsome Temper, which requires a large mana investment, try Madcap Skills maybe? I'm not sure how your meta looks like but a 4x Doom Blade is probably not the best idea when you are against any deck that runs black. Sure, you'll still have targets in Mutavault, but oftentimes you might find yourself wishing that you would actually like a Bile Blight, Devour Flesh, or Ultimate Price.

Mizzium Skin is probably the better replacement if your creatures are getting Doom Blade'd, Gigadrowse is definitely better than Blustersquall IMO despite the more intensive mana costs. If your opponents' creatures are too big for you, definitely try counterspells like Essence Scatter, Mana Leak, Pongify, or Rapid Hybridization. Hypersonic Dragon is a good evasive beater, so it's a good choice. The Sorcery-speed-at-Instant ability is just gravy.

If you don't have enough creatures, cards like Young Pyromancer might also help muck up the ground with chump blockers until you get your big dudes out. As always, more draw spells is better than less draw spells, as it will help draw you into the gas you need.

Charmbreaker Devils are nice but you definitely don't need 4, especially with their mana cost - the same goes with Devastation Tide. I'd say take out Devastation Tide completely, and maybe leave 1 or 2 Charmbreaker Devils in at most - you don't want them cluttering up your hand early on when you want to be laying on the beats early and blocking them. Since you want to cast as many spells per turn as possible for Nivix Cyclops and/or Spellheart Chimera, you may also want to take out Hostility.

That leaves you with some slots to replace stuff with. The typical Izzet pseudo-storm deck includes Guttersnipe and Kiln Fiend - if the people you go against like to clutter up the board a bit, you may want to try Wee Dragonauts as well. Even Gelectrode functions well in this type of deck, but you already have a lot of 3-drops with Nivix Cyclops and Spellheart Chimera.

You also seem to be highly lacking in the amount of draw spells you have - you can't particularly go crazy with spells if you're only drawing a card per turn. Look at Red or Red/Blue card draw, specifically Faithless Looting or Izzet Charm. Faithless Looting lets you dig 4 cards deep into your deck, letting you discard your lands once you don't need them or discard redundant cards; meanwhile, Izzet Charm allows for versatility in what mode you want in addition to letting you dig for cards. On the blue side, if you're just doing this casually, try Ponder or Brainstorm - both are great cards, but are banned in Modern formats. These are more on the expensive side, though. If you want more ways to ensure that you get more spells, Magma Jet, Preordain, or (if you're crazy) Mystic Speculation allow you to ensure that you're constantly drawing the cards you want.

You have a lot of ways to get rid of stuff your opponent plays, or to burn them to the face - but it might be too much. Try removing a couple of the less-good spells (in order of to-be-removed): Blustersquall, Curse of the Swine, Pillar of Flame, and MAYBE Thunderbolt / Turn // Burn. Teleportal is great for punching through, but three mana is a lot when you want to fill up your grave/spam a bunch of spells quick. More options to get your dudes through would be Artful Dodge, or Distortion Strike. Both are cheap ways to ensure your guys are unblockable. I would also include spells to protect your creatures - Mizzium Skin is a good card for this. You also might want to look for cheap counters - Condescend is great for a flexible counter that lets you filter out cards you don't want (Stymied Hopes is similar in this regard), Dispel, Turn Aside, or Spell Rupture (Especially if you have a Nivix Cyclops out - they have to pay 4 to counter it if it's the first spell you cast this turn).

These are all suggestions, of course. They would take your deck from going to a midrange-y, incremental advantage-type deck to a full-on spellspam deck, which may not be what you want.

I dunno about your budget, but Entomb and Buried Alive are good at getting creatures in your grave to target with Hell's Caretaker. Good targets that put creatures on your board for more sacrificing are stuff like Grave Titan, or if you're poor, Maalfield Twins. Decent early game creatures to sac them too would be stuff like Festering Goblin or Blistergrub.

For synergy with Skirsdag High Priest, maybe try stuff like Wakedancer, Skeletal Vampire, Marsh Flitter, or Dread Drone? Abhorrent Overlord can be a useful Entomb/Buried Alive target too.

There are a couple directions you can take this deck, depending on what you want to replace/what you like:

5 Color Ramp: Peregrination, Explore, Exploration, Kiora, Karametra, Tooth and Nail, etc. Heavy green base. Focusing on getting your fatties + Progenitus out as fast as possible to beat face. Find every land ramp card, plus a couple protection cards (Privileged Position, etc.), and throw in your favorite fatties. In terms of removal, a couple of Red or Black board wipes (Black Sun's Zenith, Pyrohemia, etc.) would be good here, as well as more expensive board wipes (Decree of Pain, Plague Wind, Merciless Eviction).

5 Color Dragons: Have Scion of the Ur-Dragon as your commander. Throw in every dragon you can find, add some more fixing, and go to town. Similar to the above strategy. Try Dragonstorm.

5 Color Colors: Sunburst cards (Etched Oracle), Domain Cards (Draco, Manaforce Mace, Allied Strategies), Basic Land Type fetching and cards(Krosan Verge, Shocklands, Burnished Hart), and cards that care about how many colors a card has (Civic Saber, Knight of New Alara). Throw in as many unwieldly, but useful multicolored creatures you can find (Sen Triplets, Tariel, Karador). Commander would either be kept at Progenitus or changed to Cromat, as they match the theme pretty well. If you want, Child of New Alara is a pretty good idea too.

Your deck looks a bit too high-curve to be running only 20 mountains - take out the Volcanic Geysers for either more mountains or a couple Teetering Peeks/Smoldering Spires, or if your budget is decent you might want something like Hall of the Bandit Lord.

I think multiple Kioras are fine - Kiora is fairly fragile and she is most likely going to die before she gets her ult off unless the opponent is voltron'ing it up.

Take a note that your sideboard should be 15 cards - I'd take out either Illusionist's Bracers or a Deadly Recluse.

I'm confused as to what your early game plan is - you have Cloudfin Raptors, which are fairly aggressive, but your two-drops - Kiora's Follower and Sylvan Caryatid - want you to go more defensive. I'd take those out for Elvish Mystics, as t1 Elvish Mystic -> t2 Sylvan Caryatid/Kiora's Follower -> t3 Arbor Colossus/Prophet is pretty brutal.

Ratchet Bomb is nice, but it should be relegated to sideboard - I'd move your dissolves or that Whelming Wave up to mainboard.

Courser of Kruphix is great where it is, as it smooths out your draws but it's not exactly something you want to be drawing in to late game. The Bident is an awkward spot - by the time it comes down, you won't want to attack with more than one creature, but you don't have enough early strength (other than maybe the Cloudfins) to consistently get in for the damage by the time you put it down. I'd also add Polukranos in place of the Bident and Oracle's Insight, in order to get some more permanent removal in your deck - despite all your bulk around t4-5, you can't reasonably get through, say, a Boros Reckoner unless you land one of your fliers.

If you want to move your deck to a more midrange-oriented deck, load up on those Polukranoses/Horizon Chimeras as well.