Any suggestions on this deck are welcome. I've been tweaking it since Theros came out and I saw Spellheart Chimera. The main problem matchups are currently UW control and monoblack devotion, though it can usually struggle out game 1 victory vs MBD and it sideboards well against most everything.
I love Spellheart Chimera, and I love scrying. This deck uses both, along with one of my favorite planeswalkers, Ral Zarek, who makes both a wonderful control burn/ramp engine and a wonderful alternate win condition. Scry gives this deck an absurd amount of consistency; if you don't believe me, try it. Given the slowness of the format (comparative to what I'm used to, at least), you just need to knock things down and scry for what you want next.
Now, as for individual card choices:
For disruption, Dissolve and Counterflux are pretty standard, and the numbers can be tweaked, though the scry on Dissolve is actually quite important for the consistency of the deck. Thoughtseize (and in the sideboard, Duress) are just hand disruption, in a similar vein. You'll notice that we don't have a lot of turn 1 black mana, but that's okay; generally, we don't usually want to Seize until turn 2 against control, and our matchup against aggro is so hilariously in our favor that it doesn't much matter there. (We'll be siding them out vs aggro, anyway.) Duress in the sideboard helps you neutralize control.
Every mode of Izzet Charm is relevant. Picking off, for instance, Dryad Militant is incredibly important in a deck that cares about the graveyard, along with high-damage weenies like Fabled Hero. Of course, don't be hesitant to blow it on something less valuable, the goal here is to go one-for-one most of the time and avoid damage. The counter effect is, well, more disruption. And draw two; discard two can put up to three extra spells into the graveyard to power up our Chimeras. (It can also be used to search for a much-needed Dreadbore or Anger of the Gods.)
Our removal suite is Anger of the Gods, Dreadbore, and Magma Jet, providing ways to deal with large hordes of small creatures, creatures that care about the graveyard, and planeswalkers. In game two, if the opponent's not playing black, we will usually also be siding in Doom Blade, but monoblack devotion is too prevalent in the meta to mainboard them. If we really need to remove a god or an Obzedat, Ghost Council from someone's deck, that's where we also add in Turn / Burn.
For draw spells, Thoughtflare is close to a Sphinx's Revelation effect, though it digs much further for much less cost. In a pinch, you can also pitch instants and sorceries to power up Spellheart for lethal. Divination is, well... Divination. I'm currently trying a build without Read the Bones but it's a good option; often scry 2 is worth the two life.
As for creatures, the deck centers around powering up Spellheart Chimera, which will usually come out at 5/3 or 6/3 flying trample. Sometimes even more; against janky mill decks or long-game board stall control decks, they can be swinging for 10-15 damage. For three mana. With double evasion. The two Stormbreath Dragon are fantastic value, offering both another insurmountable obstacle for white decks to climb over and an incredibly fast win condition. (Usually you'll drop it and then monstrosity it next turn, oftentimes this is enough to win right there.)
Ral Zarek is a bit more complicated in his usage patterns. Often we'll want to cast him right away at 4 mana, but it depends heavily on the board situation and deck. Sometimes, putting him out and then +1ing him to untap a land to open counter mana (or another spellcast) is what we're looking for, and sometimes we just put him out and bolt something. He acts as both a bolt engine (hitting the enemy for 3 for a few turns to push to victory, or removing creatures/pushing our removal to where it kills things like Desecration Demon) and a win condition (if you resolve that ultimate, you're probably going to be able to drop a flyer and win before your turns are up.)
Lastly, we have the fringe card Hammer of Purphoros, a one-of (you never want more than one, and it's very, -very- fringe but hilarious when you get it working) that can completely and utterly upend the control and midrange matchups. It's ridiculous. Early on, your Spellhearts can become Ball Lightning. Later, you just start eating your land and begin laying the beats.
