So I was thinking a while back about a cycle of MDFCs with a tap dual land on one side and a spell of those two colors on the other.
While I wish there had been common MDFC lands in Zen for pauper, I don't think I can justify these at common and I don't want to go so complex as them being rare, so I'm shooting to land at uncommon for this cycle. I also want the abilities to be more niche, either sideboard-like effects or so that they aren't just "auto-include" in every deck of the color pair. I'm still thinking through ideas for different pairs, so if you have thoughts, let me know.
Destroy target artifact or enchantment.
Sylvan Veld enters the battlefield tapped.
T: Add G or W.
Arcanum Devourer 1UR
Creature - Elemental
Whenever you cast an instant or sorcery spell, put a +1/+1 counter on CARDNAME.
Sea-Ringed Peak enters the battlefield tapped.
T: Add U or R.
Viable sideboard cards would be the definition of an auto include for this type of effect. Instead you probably want a signpost card. Somwthing that isn't bad but you wouldn't actually want if not playing that strategy.
Disentangle would be an auto include because you could always use land and a random disenchant is game breaking in the right situation.
Arcanum devourer is closer but the play instants and sorcerys is a more all the time for red and blue rather than a specific set signpost.
The land side of these is quite strong alone. Compare to the mythic cycle from ZNR. The lands here seem like they might be better than those and all of the other land sides of the ZNR cards are weaker than those. The problem being that the more powerful the land side the weaker the other side needs to be, and you don't want the nonland side to be too overcosted or it's not as fun to play with.
The land sides here are something that is pretty common with an upside at common (Alpine Meadow/Bloodfell Caves), so a generic ETB tapped land back side shouldn't be a problem at uncommon. I was actually surprised there wasn't at least a cycle of the MDFC lands at common in ZNR, with cards like Floral Tetrahedron or Skyclave Cleric.
Yeah, figuring out the right balance point for these is tricky. Most of the uncommon backsides have spells that would be considered just the underpowered side of "fair", like how Khalni Ambush or Kazuul's Fury are basically 1 mana more than typically common cards.
My though with these was that Disentangle would be fair as a two color Disenchant/Naturalize and especially Nature's Chant, since the cost is very restrictive and you cannot use the land side as fixing if you want to cast the spell side. It is quite consistent in a deck that is fairly even between green and white, but its bad for a deck of one color that wants to splash the other.
Similarly, Arcanum Devourer is (almost) just Spellgorger Weird with a more restrictive cost.
Figuring out how mush of a "cost" the specific mana requirements are is a challenge.