I'll admit, I'm so disappointed you didn't name that card Factory Fiction

Mishra's Factory + Shoreline Salvager

Forgotten Slough
Land - Swamp
: Forgotten Slough becomes a 2/2 black Surrakar until end of turn.
: When a Surrakar you control deals combat damage to a player this turn, draw a card.

Shoreline Salvager + Treasure Mage

Forgotten Finder
Creature — Surrakar
When this creature enters, if you control an Island, search your library for a card with mana value X, where X is the number of Islands you control. Reveal that card, put it in your hand, then shuffle.
The surrakar have not been seen since the Eldrazi war. That is their preference.
2/1

treasure mage + urza's power plant

Urza's Power-Plant + Raging Ravine

Urza's Plant Power
Land Creature - Urza's Plant Elemental
Urza's Plant Power enters the battlefield tapped
Whenever Urza's Plant Power attacks, create X 1/1 red and green plant creature tokens for each Urza's land you control.
[2/2]

Raging Ravine + Pillar of Flame

Cloister of Peace
Land (R)
This land enters tapped unless you control two or more other lands.
: Add .
: This land becomes a 1/1 white Cleric creature until end of turn. It's still a land.
As long as this land is a creature, it has "If another creature would die, exile it instead."

Manlands as a downside? I could see this being a neat cycle.

pillar of flame + crash landing

Scorn of the Spirits
Sorcery
Scorn of the Spirits deals damage to target creature equal to the number of cards you own in exile. You gain that much life.

crash landing + vault 87: forced evolution

Vault 87: Forced Evolution + Dauthi Embrace

The Madness of Between
Enchantment — Saga
I, II, III - Each player puts a shadow counter on up to one creature they control.
IV - Target player gains control of all creatures with shadow and sacrifices all creatures they control without shadow.

dauthi embrace + exile

Corruption of Shadow
Instant
Target creature gains shadow until end of turn. At end of turn, if that creature attacked or blocked this turn, exile it.

Exile + Once Upon a Time

All Alone
Instant (R)
X is the number of creatures on the battlefield minus one.
Exile target creature.

Once Upon a Time + Prairie Stream

Diluvial Plain
Land
: Add or . You can't activate this ability after your fourth turn this game begins.
: Add . You can't activate this ability until after your fourth turn this game begins.

prairie stream + wolf in _____ clothing

Wolf in _____ Clothing + Spitting Image

Unstable Facsimile
Enchantment (R)
At the beginning of your end step, put a decay counter on Unstable Facsimile, then create a token that's a copy of target creature except it has "This creature gets -1/-1 for each decay counter on Unstable Facsimile."
Barbara watched in horror as her husband's face began to sag off his bones. "Barbara, what's wrong?"

spitting image + recoup

Trace
Instant
Copy target spell. If this effect creates a token, sacrifice that token at end of turn.

Retrace

recoup + dirtcowl wurm

Dirtcowl Wurm + Leyline of the Void

Gluttonous Wurm
Creature - Wurm (U)
Trample
This creature enters with five +1/+1 counters on it.
Remove a +1/+1 counter from this creature: Exile target card from a graveyard.
0/0

Leyline of the Void + Blightwidow

Leyline of Blight
Enchantment
If this card is in your opening hand, you may begin the game with it on the battlefield.
All damage is dealt as though its source had infect.

Blightwidow + Qasali Pridemage

Leonin Purifier
Creature - Cat Wizard (U)
Whenever a creature you control attacks alone, put a wear counter on each artifact and enchantment defending player controls. (Then destroy each permanent with a number of wear counters on it greater than its mana value.)
2/2

Qasali Pridemage + Scourge of Valkas

Dromoka's Thunderhead
Creature — Dragon
Flying
Whenever Dromoka's Thunderhead or another Dragon you control enters, choose any number of target artifacts, enchantments, and/or cards in a graveyard with a total mana value equal to that Dragon's toughness. Exile those permanents and cards.
Before Dromoka, all the land will be scoured of the taint of foul magic. All that remains will be her family.
4/4

Scourge of Valkas + Lord of Atlantis

Atlantean Drowner
Creature - Merfolk Rogue
When ~ or another Merfolk enters under your control, return target nonland permanent with mana value X or less to its owner's hand, where X is the number of Merfolk you control.
Even dragons can drown if they are dragged down deep enough.
[2/2]