With the recent printing of Sovereign's Bite I think that the Black Burn fringe archetype might actually have enough cards to form a semi-viable deck.
The deck is almost Mono Black with a micro-splash for Lightning Bolt (too good to pass) and some SB cards.
The deck has a lot more lifegain (16x spells) compared to a typical Burn deck which can let it go longer and trade life against other aggro decks.
Another card which might be worth splashing here is Skullcrack (or Rain of Gore/Flames of the Blood Hand) for the SB though not sure how important lifegain hate should be in this build of Burn.
I've played regular Burn for quite a while, so I'd like to comment from that perspective. In principle, the question you need to answer is "why is this better than Boros Burn?" (provided that you care about winning). The main issue with Boros Burn, I think, is that its curve is slightly too high to be consistently fast enough and/or cheat on land more to prevent flooding. In my experience, regular Burn dies to flood or clunky slow hands with too many 2 mana spells far more than getting mana screwed on 1 land (provided that you only keep 1-landers with a decent number of 1-drops, of course). The problem with 2 mana spells is that it takes 4 mana to double spell with them and that takes way too long.
This deck has an even higher curve (especially without the discard synergy in place), not to mention slow creatures of 2 mana without haste or otherwise guaranteed damage. Even though there's quite some life gain in here, Burn rarely loses the race because of a lack of life gain, but rather because it can't unload fast enough to race a combodeck or a 'control' deck that simply stabilizes through blockers/counters/discard at too high a life total to easily topdeck out of. Sure, you'll win games because all your 'burn' spells gain you life that you wouldn't have if they didn't, but the question is whether you'd have also won that game if these spells simply cost half the mana and were cast way quicker. Not to mention that a big incentive to play Burn is Searing Blaze which is an insane tempo swing.
That said, I think Rb Burn may have legs, if you only use the 1 mana black spells instead of the white 2 mana spells.
The problem with this, imho, is that the white spells offer you good interaction to win a race/break up a combo (Lightning Helix and the highest damage in a single card for 2 mana (Boros Charm) + good sideboard cards like Rest in Peace and Deflecting Palm. For the small benefit of being slightly easier to cast, Sovereign's Bite is just a much worse Helix. Also, Gonti's Machinations isn't guaranteed damage on a topdeck which is usually a big no-no in burn-style decks.
Alternatively, exploiting Bloodchief Ascension may seem more useful in a black shell that also includes Blightning and other discard, as mentioned above. I'd stay away from cards that give your opponents the choice, though. The margins in Burn are so slim that you can't afford to hand them the reigns.
I continue to be very leery of Energy mechanics in Modern. Because Energy has only been used in one set, you don't have enough cards with high enough powerlevel to get a critical mass in Modern. I am skeptical that Syphoner will be able to draw cards routinely or that you'll be able ot activate Machinations routinely enough without more Energy cards and there aren't more energy cards to add. I would remove them.
Even if Black is the primary color you'll want a splash of another most likely. Battlefield Scavenger might be a good enough Rogue that also enables Madness, but you might also look at the Blue as the splash and see if you can make a "Black Burn" that is Bu with a Rogue subtheme.
But to be better at burn than burn,R3Dox is correct... You have to better than Burn at something and or fix some of the issues with Burn. Rogue subthemes help you to draw more cards with spells like Morsel Theft. That could be the improvement you are looking for. Bitterblossom not only enables the Prowl mechanic well, it also becomes a forcefield spell that might add a couple turns against some decks.
I will caution that people have been trying to make Rogues work for a very long time, and its very difficult to do. The creatures are fragile and enabling Prowl is very hard in Modern.
I wonder if Rotting Regisaur is the creature that can upgrade this deck as it helps enable Alms and is a very fast clock.
It can replace Geralf's Messenger but Oona's Prowler seems like a better cut though it would make the deck far slower with so many 3-drops.
Been trialing Regie in mardu midrange alongside souls and Smiting helix. And he's pretty solid but he is a do nothing the turn he comes down. In midrage there are alot of targeted discard ect to make help him stick for a turn but in burn where you what all the cretures to do stuff the turn the hit he may be a little less reliable. If you decide not add him it might be worth keeping messager in and adding a couple of flings/thuds?
Also for consistant card draw have you considered Stormfist crusader?
I'm not sure that I like the symmetrical card draw of Stormfist Crusader.
There is always the option of Dark Confidant but it isn't really much of a threat (Siphoner at least has menace).
All I need is one attack from Regi to get value, I'll need to see how it works in the deck.
The deck is almost Mono Black with a micro-splash for Lightning Bolt (too good to pass) and some SB cards.
The deck has a lot more lifegain (16x spells) compared to a typical Burn deck which can let it go longer and trade life against other aggro decks.
About the card choices here:
# Glint-Sleeve Siphoner + Gonti's Machinations fuel each other to generate energy and become basically an evasive Dark Confidant and a 1-mana Helix (which only targets players).
# Oona's Prowler - a cheap evasive beater which enables "madness" for Alms of the Vein.
# Sign in Blood - draws cards to keep the deck going, triggers Machinations and can finish games as a "Shock" to the face.
# Geralf's Messenger - a resilient creature threat with a life-drain EtB ability, basically a much better Keldon Marauders here.
# Collective Brutality - does pretty much everything and provides interaction with spell-based combo decks.
Here is the list:
4x Glint-Sleeve Siphoner
4x Oona's Prowler
4x Geralf's Messenger
Instant (4)
4x Lightning Bolt
Enchantment (4)
4x Gonti's Machinations
Sorcery (18)
4x Bump in the Night
4x Collective Brutality
4x Sovereign's Bite
2x Sign in Blood
4x Alms of the Vein
4x Bloodstained Mire
4x Polluted Delta
1x Blood Crypt
1x Smoldering Marsh
1x Leechridden Swamp
10x Swamp
1x Urborg, Tomb of Yawgmoth
4x Inquisition of Kozilek
4x Fatal Push
2x Nihil Spellbomb
2x Contaminated Ground
2x Rakdos Charm
1x Blightning
Another card which might be worth splashing here is Skullcrack (or Rain of Gore/Flames of the Blood Hand) for the SB though not sure how important lifegain hate should be in this build of Burn.
This deck has an even higher curve (especially without the discard synergy in place), not to mention slow creatures of 2 mana without haste or otherwise guaranteed damage. Even though there's quite some life gain in here, Burn rarely loses the race because of a lack of life gain, but rather because it can't unload fast enough to race a combodeck or a 'control' deck that simply stabilizes through blockers/counters/discard at too high a life total to easily topdeck out of. Sure, you'll win games because all your 'burn' spells gain you life that you wouldn't have if they didn't, but the question is whether you'd have also won that game if these spells simply cost half the mana and were cast way quicker. Not to mention that a big incentive to play Burn is Searing Blaze which is an insane tempo swing.
That said, I think Rb Burn may have legs, if you only use the 1 mana black spells instead of the white 2 mana spells.
The problem with this, imho, is that the white spells offer you good interaction to win a race/break up a combo (Lightning Helix and the highest damage in a single card for 2 mana (Boros Charm) + good sideboard cards like Rest in Peace and Deflecting Palm. For the small benefit of being slightly easier to cast, Sovereign's Bite is just a much worse Helix. Also, Gonti's Machinations isn't guaranteed damage on a topdeck which is usually a big no-no in burn-style decks.
Alternatively, exploiting Bloodchief Ascension may seem more useful in a black shell that also includes Blightning and other discard, as mentioned above. I'd stay away from cards that give your opponents the choice, though. The margins in Burn are so slim that you can't afford to hand them the reigns.
Even if Black is the primary color you'll want a splash of another most likely. Battlefield Scavenger might be a good enough Rogue that also enables Madness, but you might also look at the Blue as the splash and see if you can make a "Black Burn" that is Bu with a Rogue subtheme.
But to be better at burn than burn,R3Dox is correct... You have to better than Burn at something and or fix some of the issues with Burn. Rogue subthemes help you to draw more cards with spells like Morsel Theft. That could be the improvement you are looking for. Bitterblossom not only enables the Prowl mechanic well, it also becomes a forcefield spell that might add a couple turns against some decks.
I will caution that people have been trying to make Rogues work for a very long time, and its very difficult to do. The creatures are fragile and enabling Prowl is very hard in Modern.
I just happen to run some because they enable some synergies within the deck and have evasion to get damage through.
I don't expect this to be better than traditional Burn because this is highly unlikely to happen, just to be the best version in its colors it can be.
It can replace Geralf's Messenger but Oona's Prowler seems like a better cut though it would make the deck far slower with so many 3-drops.
Also for consistant card draw have you considered Stormfist crusader?
Competitive Decks
Devotion to the Lash B ----
Monkey Conservation WUGR ---- Dragon WorshipR
There is always the option of Dark Confidant but it isn't really much of a threat (Siphoner at least has menace).
All I need is one attack from Regi to get value, I'll need to see how it works in the deck.