Izzet Metabreaker (Hullbreaker) (Standard)

Prismari Command over Unexpected Windfall: The deck wants to ramp into the dragon more often than it wants to ramp into anything else (since I cut epiphany to try sth new)
Syncopate over Saw it coming or disdainful stroke: while 2 mana counterspells work great with goldspan on turn 5 and onward, syncopate can help topple the opponent in the early game alongside jwari disruption. It's particularly good on turn 3 or 4 if you can keep up another instant speed spell too. Of particular note is that it can be played alongside hullbreaker Horror for one mana as a remand.
Syncopate doesn't protect goldspan dragon well the turn he is played though, so I added some copies of negate, which I feel are good in a deck protecting some queens.
Burn Down the House or Battle of Frost and Fire?: Without galvanic Iteration there is no particularly good reason to play burn down the house, unless you run the egg in the mainboard. We will see how big the important meta-creatures are gonna be. Battle of Frost and Fire might be slow, but with goldspan dragon the deck is not depending on the devil tokens anyway. Hard choice still, since those could be used as blockers too especially if goldspan dragon is on the board. On the other side Battle of Frost and Fire can be bounced and replayed for additional value (potentially even with the trigger on the stack during upkeep). Although i doubt this is gonna come up a lot once the hullbreaker horror is on the board.
Cinderclasm: Without galvanic iteration this card is gonna be dead more often than it used to be. Still: 1 or 2 damage at instant speed seriously punishes mono-white.
Dragon's fire over Cathartic Pyre: I figured that potentially doing 4 damage is more useful than the loot. The card still works with hullbreaker, since you can always just target him/her.
Hullbreaker Horror: Finisher type card. All the small spells like Spikefield hazard are now remands.
Maybe one could replace some copies of expressive iteration with consider? But the former is just strong, while the later just works well with hullbreaker horror.

Matchups:

Mono-White: should be crushed hard. Spikefield-hazard, cinderclasm and some more interaction that works alright like fading hope, prismari command and dragon's fire. Little to no removal on their part makes cleaning up in the end-game particularly easy I predict.
The counterspells are mostly dead, although new iterations of mono-white run maul of the skyclaves

Mono-Green: A lot harder. Spikefield is mostly a tapped land. Cinderclasm would be better as a demon bolt or so. Against all the value cards bounce and stall is more important. On the upside syncopate is more effective since mono-green plans to curve out more often and plays more expensive threats. Negate hits valuable targets.
We are gonna see whether Green is gonna adapt some of the new 4 to 6 mana creatures. Some of them offer strong board wipe protection.
Most notably goldspan dragon is a weird card against mono-green. They can kill it pretty easily, and this deck offers no follow up in form of epiphany anyway. Also doesn't provide chump-blockers.

Izzet Turns: I could see this being a winning matchup. Some counterspells go a long way. But most notably this deck can bounce spell copies into oblivion once the hullbreaker horror is on the board. Besides winning before the hullbreaker horror comes down all izzet turns can do is bounce him/her back to the hand. Luckily the guy/girl has flash so there are many situations where you might flash him/her in and have a counterspell ready to answer epiphany plus hitting the copy with hullbreaker horror. Obviously this is easier to do with disdainful stroke or test of talents than it is with syncopate. One of the reasons why playing goldspan dragon is such a good idea, since he/her burns up some bounce spells and provides mana along the way.

Other control: Hullbreaker is a strong endgame, being uncounterable. Azorius has only a little targeted removal to fear and is mostly prepared for sorceries currently. Hullbreaker horror seems like a strong sideboard card against control decks in general though.

Vampires/Werewolfs?: A good amount of instant speed interaction to react to haste is good. The big problem is gonna be handling different forms of protection and value engines in those decks (board wipe protection in red and green; florian that punishes players not blocking early; Immersturm Predator how needs to be bounced and blocks goldspan dragon well; wolves producing more wolves etc.). This makes cinderclasm and battle of frost and fire weird to evaluate.