vision skeins/fanatical devotion

Shared Devotion
Instant
Creatures gain hexproof and indestructible until your next turn.
Each player draws a card.

Fanatical Devotion + Birchlore Rangers

Birchlore Rangers + Scavenger Folk

Birchlore Scavengers
Creature — Elf
, , Tap two untapped Elves you control: Destroy target artifact.
1/1

Scavenger Folk + Gleancrawler

Scavenge Crawler |
Creature - Insect

Exile ~: Return to your hand all creature cards in your graveyard that were put there from the battlefield this turn.

1/1

Gleancrawler + Detonate

detonate/mirrorworks

Mirror Foundry
Artifact
Whenever a nontoken artifact enters the battlefield, you may create a token copy of it. If you do, ~ deals damage to you equal to its converted mana cost.

Mirrorworks × Mountain (HOU)

Mountain + Simic Growth Chamber

Flooded Valley
Land (R)
Landfall - Whenever Flooded Valley or another land enters the battlefield under your control, add , , or .

Simic Growth Chamber + Daring Demolition

Daring Demolition + Elfhame Druid

Rapid Reclamation
Instant
Kicker
Destroy target artifact. If that artifact was a Vehicle, destroy each creature that crewed it this turn. If that artifact is an Equipment, destroy the creature it's attached to.

Elfhame Druid + Pardic Swordsmith

Duergar Druid |
Creature - Dwarf Druid

, Discard a card at random: Add to your mana pool.

Shrooms. Trees. Same difference.

1/1

Pardic Swordsmith + Magmatic Force

Magmatic Force + Plains

... seriously?

Serra's Grand Cathedral
Legendary Land
At the beginning of each upkeep, add . Until end of turn, you don't lose this mana as steps and phases end.
The heart of Aysen still shines.

You guys really enjoy making busted lands don't you.

Plains × Blood Seeker

It doesn't give you mana the turn you play it, doesn't give more than one mana a turn, and is legendary with no subtype to tutor. It's possibly a lot of advantage, especially in multiplayer... if and only if you can consistently capitalize on getting a single free off-turn.

I dunno, maybe my land balancer is just far off to the point where if it doesn't give you a mana RIGHT NOW it's pretty heavily crippled.

Blood Seeker + Punishing Fire

Chivalrous Spellthief

Creature - Human Rogue
Whenever an opponent gains life, you may pay . If you do, return target instant or sorcery card with converted mana cost less than or equal to the amount of life gained from your graveyard to your hand.
"Steal from the wise and conjure for the poor."
1/1

Lands that can produce mana without being tapped are generally pretty busted, because you can exploit them with Urborg or other equivalent effects. It was equally addressed to Rush's landfall land, which is probably even better.

Punishing Fire × Storm Shaman

Storm Shaman + Secluded Steppe

Firestorm Shaman
Creature — Human Shaman
: Firestorm Shaman gets +1/+0 until end of turn
Cycling . Spend only red mana on this cycling cost.
Whenever you cycle this card, target creature gets +X/+0 until end of turn.
0/4

secluded steppe/bat token

Night Terror
Creature - Bat Horror
Flying, Lifelink
~ can't block.
Cycling
3/1

Secluded Steppe × Mons's Goblin Waiters


Bat Token × Mons's Goblin Waiters

I misinterpreted the rules and thought you could choose which new card to meld with the previous one, instead of random. Not sure if my version would make a good game