Here's what I have planned for Theros. I have this listed under Budget because I'm on one and sadly I don't even have enough for Reckoners and I don't feel comfortable splashing White when I can't afford shocks either.
I'm not sure what to fill the rest of the sideboard with at the moment.
After realizing that Thunderbolt was NOT reprinted, I now have 4 open slots available and I don't know what to put in it's place. I'm afraid to splash white without shocks otherwise I would happily make room for Warlord's Helix and Boros Charm. Gates are too slow and we'll have to see what lands Theros brings.
The deck as it stands right now is well, a burn deck, which uses all of the 2 mana for 3 damage burn spells available as well as Shock and Magma Jet. Shock because it's cheap and instant speed, and Magma jet because it's Magma Jet. Young Pyromancer is an obvious choice and will most likely be creating blockers more than attackers, but can obvious do the opposite as well. Wild Guess is my choice of hand filling because it goes oh so well with Chandra's Phoenix, which I can easily return to my hand. The 4 Reverberates main board is to give me another set of 2 for 3 Damage and for getting another 2 cards from Wild Guess, which draws me 4 cards in total, something burn players like. Ash Zealot is a good haste bear here with First Strike, which is just icing. Ideally, we want to sit on 4 lands to cast two spells a turn, but having 5+ isn't bad because we can drop Phoenix/Zealot late game or Wild Guess into a shock and bringing back Phoenix at 6 mana or something.
The sideboard is fairly simple right now, but as I said before, I don't know what to fill the rest with. Peak Eruption is to bring in against other Red decks, which is just value (also another good reason to keep reverb Main board if someone pulls it on me), Mind Sparker for U/W, though I'm not entirely sold on it costing 3 mana with no immediate value. Awaken the Ancient is a solid finisher that I can pull out of Side Board after certain charms are boarded out since I don't run anything bigger than 2/2 main board. Depending on the size of certain creatures, I'm thinking about Chandra's Outrage as a possibility.
On the note of certain things that are missing, Chandra in particular. I don't think I need her honestly. Four mana is a lot in a deck where that's the top and she doesn't do enough for me when she drops as much as I love her. However, Burning Earth is something that I would love to include and might tuck it into the side board, but I don't know if there's anything else that I should put in instead. The reason it's not main board is that it is a little slow, and I can't take the risk of having one in my hand and not being able to cast it. On top of that, since this is post rotation planning, I'm counting on a ton of enchantment hate being packed because of the Gods and whatnot.
Anyway, if you think I missed anything, let me know. I'm always open to criticism.
Yea I know, I realized that after I made the thread and have since edited it. I could have sworn I saw it in M14. Oh well.
I have considered Flames as a replacement. I just don't like that it's 3cmc with only 20 lands. I could run 3 with 21 lands, but I don't want to run the risk of getting flooded out. Maybe I'm being too paranoid.
I'll reiterate a question I added after I realized TB was not reprinted:
How doable is it to splash white without having any Shocks? Gates seem too risky, and we don't know what we're getting out of Theros.
I am also thinking about Frostburn Weird because it slows down aggro and is a mana dump later.
What about Guttersnipe?
If you like haste options, Rakdos Shred-freak is the first that comes to mind. You're running one color so it's mana cost won't be too much of a problem plus it's another T2 play.
Your curve maxes out at like, 3, so I think it might also be a good idea to throw in some T1 plays like Rakdos Cackler. You'd probably rather cast shock T1, and that's fine, but i think the cackler would give you a cheap option to chump if you really need to (just don't unleash it unless it's early game)
The only problem with my suggestions is that there's not a lot of room and your deck seems solid as it is...
As for your sideboard, my first thought is "what if blue bounced all of your **** then countered it when you try again," but that can't bee too much of an issue either since you have such cheap cards, plus the Phoenix gives itself back.
since Sideboards don't have to be exactly 15 anymore, it can't be too much of an issue. Though you could totally fill out the rest with lands cause why not lol
as for splashing white, i don't think it's too hard. just remember to keep your curve low since that's what your aiming for. In fact, I'd say keep white in your sideboard since you're focusing a LOt on Red main board, and yo udont' want to muck it up too much.
On the gates, yes, they're risky ESPECIALLY in a 20-land deck, nd in fact, if you really wanted to splash White i'd suggest going back to 24 or 23 lands with 2 or three being gates with a few plains.
You're going to need something that can take care of creatures bigger than 3/3. Don't really want to waste 2 spells to kill 1 creature even with Young Pyromancer out. Burn as of now isn't as fast/efficient as it should be, so you really can't race a midrange deck before they're able to stabilize. I tried the list (minus the Theros cards, replaced them with counterparts about to rotate) vs a Selesnya midrange deck with Trostani, Centaur Healer and Advent of the Wurm, it felt like I just can't win.
Mizzium Mortars or Chandra's Outrage? Ratchet Bomb can take care of tokens. Maybe Barrage of Expendables + Act of Treason (you may not even need Treason, Lightning Strike + sac the elemental created on casting it = 4 damage)? That or add white and get rid of some spells with RR in them.
I really like Lobber Crew as an inclusion even without multi-colored cards. With multi-colored cards, he's like a more durable, more situational Guttersnipe. Unlike Guttersnipe he can take a hit and help slow down aggro and regardless or whether you are laying down creatures or just holding up mana he can still tap for 1. I would take him out against control where you want to try and speed yourself up, not slow them down.
I might also suggest looking into Goblin Arsonist. His death only pings for 1 but thats after a chump block, essentially buying you that much life in the process and maybe taking out a dork or just getting you that much closer. If you can swing a couple times with him even better. I would put the Arsonist in against aggro where he could become a 2-for-1 and against control where he is fast enough, but little enough of a threat to not get immediate hate and then still gets some extra value after dying to a board wipe. He would come out against mid-range where his stats are totally irrelevant.
I've also been planning on maybe trying a burn deck (I happened to be lucky enough to pull a playset of Duals from boosters and trade for the proper colors). One card I've been seriously considering is Elixir of Immortality. Why? Well consider popping it after you've lain out 4 lands and cast 2-3 instants or sorceries. It essentially restocks your draws effectively modifying your threat density mid-game. With cards like Magma Jet and Dangerous Wager available that can help solve the card advantage problem. On top of all of that it helps pad you against aggro and mid-range. This becomes much more relevant if you can add Spark Trooper and Warleader's Helix because you have about 8-12 cards in the deck capable of gaining you 4-6 life each pop all the while still directly contributing to your game plan. Add in Blind Obedience and it takes it over the edge. (I'm not so delusional to think you would be able to activate Extort more than twice per game, but its a mana sink when you want it that gives you extra reach, extra resilience, and slows down opposing creature based strategies). It may only be useful out of the sideboard but I honestly believe that as a 2 or 3 of it can help plug a hole the deck has.
EDIT: Almost forgot! Burning Earth. From what I understand its been successful as of late punishing greedy good stuff decks. If you are in mono-color its even better. Now is not that bad of a time for burn especially since we have Magma Jet and shock lands. If your opponent plays even 1 untapped shockland they lose 1/10 of their life, thats 1 card you don't have to play (ish). If they drop more than one even better.
The following link is an invitation to join Pucatrade (card trading service though similar to TCGPLayer). If you follow the link then it awards me with tokens to exchange for actual cards. Thanks! https://pucatrade.com/invite/gift/86097
Guttersnipe is the obvious choice for another creature. I'm no fan of Wild Guess at all. Mizzium Mortars and Act of Treason would also be solid additions as well, as the first can act as burn when needed and sometimes as a sweeper. The second will take advantage of any opponent who plays better creatures than you do.