Power Plant Worker

{3}: This creature gets +2/+2 until end of turn. If you control creatures named Mine Worker and Tower Worker, put two +1/+1 counters on this creature instead. Activate only once each turn.

Urza's Power Plant

{T}: Add {C}. If you control an Urza's Mine and an Urza's Tower, add {C}{C} instead.

Urza's Tower

{T}: Add {C}. If you control an Urza's Mine and an Urza's Power-Plant, add {C}{C}{C} instead.

Self-Assembler

When this creature enters, you may search your library for an Assembly-Worker creature card, reveal it, put it into your hand, then shuffle.

Foundry Assembler

Improvise (Your artifacts can help cast this spell. Each artifact you tap after you're done activating mana abilities pays for {1}.)

Forest

Mine Worker

{T}: You gain 1 life. If you control creatures named Power Plant Worker and Tower Worker, you gain 3 life instead.

Crop Rotation

As an additional cost to cast this spell, sacrifice a land.
Search your library for a land card, put that card onto the battlefield, then shuffle.

Urza's Mine

{T}: Add {C}. If you control an Urza's Power-Plant and an Urza's Tower, add {C}{C} instead.