If you think a combo is worth mentioning, please tell me.
This list is an attempt to document combos that either win the game/provide large advantage utilizing a small number of cards that are possible in Red/Black. Combos that are available to every deck (purely artifact combos) (or mono color decks) and/or combos that are impractical in other colors (such as a combo that would never be used in a 5-color deck) will not be mentioned. These combos can hopefully be used to create better cEDH/High Power decks in these colors.
Additionally, because Rakdos contains black and red, please do realize that many of these combos are easier and quicker to assemble than it would appear at first glance, due to black's tutoring/searching capabilities and red's quick mana cards.
This is a first draft. I hope you enjoy! (I will provide brief descriptions of each combo.)
Worldgorger Dragon and Animate Dead
Upon casting Animate Dead, revive Worldgorger Dragon, and once the Dragon enters, exile Animate Dead and all of your lands. Worldgorger Dragon will die because Animate Dead left. Upon the Dragon dying, Animate Dead and all of your lands will return. You can then revive the Dragon and tap your lands again, giving you infinite mana, as well as infinite death/entering triggers.
Zada, Hedron Grinder, Crack the Earth, and Horobi's Whisper
There are many possible combos with Zada, including ones that are very similar. In this one, you play Zada as well as as many creatures as you can muster, cast Crack the Earth, and splice on one of a few cards, the most optimal being Horobi's. You target Zada with Horobi's, and Zada makes a copy of Crack the Earth for each other creature you control. You can then sacrifice your creatures, and any opponent who has a small board state will likely have to sac +5 lands and have to concede. (Even if they attempt to counterspell the original copy, all of the other copies will still go through unless they are somehow also able to counterspell the rest.)
Waste Not and Wheel of Fortune
Quite simple. Cast the latter with the former already out and create a large quantity of advantage.
Dragon Mage and Seize the Day
If you generally play a high quantity of fast red mana as well as extra combat spells, you will be able to somewhat consistently create a large quantity of advantage as well as resculpt your hand. Haste giving spells can also be helpful.
Madcap Experiment, Platinum Angel, and Repay in Kind
All you have to do is cast Madcap Experiment and then Repay in Kind. Though not guaranteed to win you the game, it should at least significantly damage your opponents while giving you a dangerous creature. Because you will put Platinum Angel onto the field before taking you would take any damage from Madcap, you will simply be sitting with a low/negative life total while still alive. Repay in Kind will then give everyone else a low/negative life.
