A couple more things.

Swan Song is almost uncuttable from Scapeshift sideboards. It counters everything relevant, and the 2/2 is less relevant than ever to the Scapeshift player.

I never see Molten Rain in any deck except Burn. Fulminator Mage is castable in all versions of BGx, as well as non-red black decks like BW Tokens, Faeries, etc. UWR will sometimes play Molten Rain , so I agree that it should be in here, but know that Fulminator Mage is likely the better card and is played more.

I disagree with GeminiSpartanX that Flame Slash doesn't see much play. Red doesn't play the card, but almost all versions of Twin (UWR generally has better removal options) play it because they need an answer to Spellskite in the maindeck. Twisted Image and Flame Slash serve this purpose.

A couple more things.

Swan Song is almost uncuttable from Scapeshift sideboards. It counters everything relevant, and the 2/2 is less relevant than ever to the Scapeshift player.

I never see Molten Rain in any deck except Burn. Fulminator Mage is castable in all versions of BGx, as well as non-red black decks like BW Tokens, Faeries, etc. UWR will sometimes play Molten Rain , so I agree that it should be in here, but know that Fulminator Mage is likely the better card and is played more.

I disagree with GeminiSpartanX that Flame Slash doesn't see much play. Red doesn't play the card, but almost all versions of Twin (UWR generally has better removal options) play it because they need an answer to Spellskite in the maindeck. Twisted Image and Flame Slash serve this purpose.

I've seen Spreading Seas in various decks, so I'd include it in this list. I disagree with thispersonisagenius about Brave the Elements though. Although not commonly used, I think it deserves recognition since a large portion of the creature control in modern comes in the form of targeted and sweeping burn spells. It's a good call for any white-weenie style of deck.

So I spent a good amount of time writing about the few on this list that were a little subpar and why, but when I went to post it I got an error and lost it all. The short list I had included Orb of Dreams , Imi Statue , Psychogenic Probe , Veilstone Amulet , and Shattering Blow . The main reasons for these picks were that for some (Shattering Blow, Imi Statue) there are just better options for SB cards with similar effects, and others (orb, probe, amulet) are a little too narrow to be used in any sort of meta I can think of. Orb hurts both players, so it would take a special MD for me to want to board it in (too narrow) and probe doesn't do enough on its own to merit a general SB slot imo. The same could be said of Cosi's Trickster , but it has a well-defined archtype to help it along (Merfolk). If you want more in-depth reasons for those ones feel free to ask!

I'd also like to add a few more to the list- Volcanic Fallout is an uncounterable sweeper I've seen people use instead of Anger of the Gods . We also can't forget the modern Force of Will , Disrupting Shoal which I've seen in the SB of storm decks primarily, as well as in a few other brews. Its general enough to warrant inclusion in this list I believe. Also Echoing Truth , Apostle's Blessing , and Vines of Vastwood are all cards I've seen in competitive sideboards. Hope this helps some. Keep up the good work! I think you've made a good resource here for players to use!

Oh also @ thispersonisagenius- I didn't mean to come off as saying Flame Slash isn't widely used, b/c it really does see play. I just didn't self edit enough. I just ment to say that it fills much of the same role as Dismember , which is a little more widely used due to having less color restriction, not that slash isn't used. My bad.

I've never even knew Disrupting Shoal existed >.< but I'll put it in, because as a storm card it can be very useful, considering storm is usually at a set cmc.

Whipflare from affinity?

Does affinity ever run red these days?

@ Femme_Fatale

Aye, Galvanic Blast and Whipflare .

It does. Normally for Galvanic Blast in the MD and Whipflare in the SB. Early builds also used Shrapnel Blast instead of Thoughtcast if they wanted to go the super burn-heavy route.

Kays. Whipflare it is then.

Rain of Tears Sowing Salt

Might want to use the ctrl + F function before suggesting cards tyforthevenom. I already had Sowing Salt .

i was on my phone, no ctrl f function on it

and there's no AEtherize which is sideboard tech for tron vs aggro

Unravel the Aether is a solid card to deal with Keranos, God of Storms , which every UR deck is bringing in/maindecking nowadays.

Speaking of which, the God of Storms himself should be in here.

Unravel the Aether would go in, but why would Keranos, God of Storms go in when he is a mainboard win condition and not a sideboard card?

And can someone else confirm AEtherize for tron? It just feels far too expensive to deal with an aggro build.

AEtherize is something I've seen once from Mono-U Tron, but I wouldn't put it in because there are much better sideboard cards.

Keranos, God of Storms is in some maindecks (usually UWR, Blue Moon and the rare UR Twin list), but most Twin decks bring him out of the sideboard. He's in sideboards much more than in maindecks IMO.

genius, name 1 card that can deal with as many threats as aetherize for u tron?

Tectonic Edge often sideboarded vs tron and other land based decks also kills the manlands before they hurt you

It isn't that AEtherize isn't useful, it's because it costs FOUR MANA to use, and by that time you are probably already done for.

Tectonic Edge is a maindeck card, or not in the 75 at all.

Even if AEtherize is the best card at that, I think as the U Tron player I am better off conceding matches to Affinity and other aggro decks so that I can have a more powerful sideboard for the decks that won't kill me before I cast a spell.

I've seen tec edge boarded in against my u tron than i've seen any other card it stops tron putting down a 4th land which slows it alot aetherize will slow affinity long enough for you to put in chalice of the void or wurmcoil

If you are using AEtherize for affinity, you are doing it wrong. You should be using Hurkyl's Recall .

I'm using his example, i use aetherize vs any aggro matchup along with plat angel steel hellkite and oblivion stone