The Deck

Ok, man, we have a pretty spicy build here... Let's get into it. The overall game plan is to cast significant burn spells and wreck everyone. The main deck is devoted to Thunderous Wrath and making sure it makes it to the top of the library using things like Opt and Mystic Speculation. Izzet is a bit different than Rakdos, but we need some ways to reduce that cost other than through a actual miracle.

The sideboard is devoted to a multiplayer Worldfire package and a nasty way to finish everyone off. Here is what I came up with.

The Burn

Regarding actual firepower, we have around 11 spells, and they all hit pretty hard. Lightning Bolt gives you some early/cheap interaction that can still reduce life totals when needed and get rid of opposing creatures should they come up. For the big guns we have Thunderous Wrath and a few copies of Banefire for those big finishes.

The Mana

If we're going to do big damage, we'll need big mana too. Anytime we can't hit the miracle cost, Thunderous Wrath will be expensive, and you want to do the biggest possible Banefire. The main card we want to draw is Irencrag Feat because it's going to cast Wrath or an x=6 Banefire as early as turn three.

However, this package (which I think we have to have) presents a problem. The "only cast one more spell" clause of Irencrag Feat means we can't use things like Dualcaster Mage since we have to cast him along with the spell we want to copy. The same is true for other spells like Reverbirate. But, I have a solution.

Copying

Instead of actually making another copy of the burn spell, we'll just make the first copy hit twice (or three times) as hard. Fiery Emancipation makes a Wrath do 15 damage, and an x=7 Banefire is game over, even if they're at 20. Solphim, Mayhem Dominus plays a similar role and is a well-costed threat himself.

If you have multiple copies, forget about having friends. Solphim, Mayhem Dominus + Fiery Emancipation + Thunderous Wrath = 30 damage. With Irencrag Feat and the Ritual, you can cast these damage enablers as early as turn 3.

Chandra, the Firebrand does many things but is mainly here for her -2, which copies spells and gets around the "only one more spell" issue because she will already be in play. For example, when Chandra is in play, you cast Irencrag Feat, make seven mana, then activate Chandra, and copy whichever spell you want to cast with the mana. You can also copy Irencrag Feat if you have do x=13.

Considering we're playing so many instants and sorceries Guttersnipe, is a must. It makes all of the burn spells better when you cast them and also gets doubled or tripled with Solphim, Mayhem Dominus or Fiery Emancipation. Say you have Fiery Emancipation and Guttersnipe in play and cast a Lightning Bolt. They take nine from the bolt and six from the Guttersnipe.

Valakut, the Molten Pinnacle Package

Last but not least, I added in two copies of Valakut, the Molten Pinnacle. When you play a mountain, if you already have five mountains (don't have to be basic) Valakut will deal three damage to your opponent. So, in total, we have 15 mountains (plus four fetches) to get this nice sub-plan online.

The Worldfire Multiplayer Suite

To kill off multiple players with Worldfire we have them in the sideboard (since they are bad in 1v1) along with Roiling Vortex. Just cast Worldfire on your turn and everyone else gets to die on their upkeep. Plus, Vortex is a great general sb card so people can't gain life and to spam extra damage that can be doubled or tripled when it hits everyone else.