Urza's Workshop

{T}: Add {C}.
Metalcraft — {T}: Add {C} for each Urza's land you control. Activate only if you control three or more artifacts.

Mishra's Workshop

{T}: Add {C}{C}{C}. Spend this mana only to cast artifact spells.

Powerstone Shard

{T}: Add {C} for each artifact you control named Powerstone Shard.

Mishra's Factory

{T}: Add {C}.
{1}: Mishra's Factory becomes a 2/2 Assembly-Worker artifact creature until end of turn. It's still a land.
{T}: Target Assembly-Worker creature gets +1/+1 until end of turn.

Sculpting Steel

You may have Sculpting Steel enter as a copy of any artifact on the battlefield.

Mishra's Foundry

{T}: Add {C}.
{2}: Mishra's Foundry becomes a 2/2 Assembly-Worker artifact creature until end of turn. It's still a land.
{1}, {T}: Target attacking Assembly-Worker gets +2/+2 until end of turn.

Mine Worker

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

Power Plant Worker

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

Tower Worker

Reach
{T}: Add {C}. If you control creatures named Mine Worker and Power Plant Worker, add {C}{C}{C} instead.

Urza's Saga

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Urza's Saga gains "{T}: Add {C}."
II — Urza's Saga gains "{2}, {T}: Create a 0/0 colorless Construct artifact creature token with 'This creature gets +1/+1 for each artifact you control.'"
III — Search your library for an artifact card with mana cost {0} or {1}, put it onto the battlefield, then shuffle.

Urza's Fun House

{T}: Add {C}.
{T}: Add {∞}. Activate only once and only if you control an Urza's Mine, an Urza's Power-Plant, and an Urza's Tower.
{7}, {T}: Head to AskUrza.com and click Urza's Fun House.

Urza's Power Plant

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

Self-Assembler

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

Adaptive Automaton

As Adaptive Automaton enters, choose a creature type.
Adaptive Automaton is the chosen type in addition to its other types.
Other creatures you control of the chosen type get +1/+1.

Urza's Factory

{T}: Add {C}.
{7}, {T}: Create a 2/2 colorless Assembly-Worker artifact creature token.

Cogwork Assembler

{7}: Create a token that's a copy of target artifact. That token gains haste. Exile it at the beginning of the next end step.

Nearby Planet

Rangeling (This card is every land type, including Plains, Island, Swamp, Mountain, Forest, Desert, Gate, Lair, Locus, and all those Urza's ones.)
Nearby Planet enters tapped.
When Nearby Planet enters, sacrifice it unless you pay {1}.

Tomb of the Spirit Dragon

{T}: Add {C}.
{2}, {T}: You gain 1 life for each colorless creature you control.

Mishra's Self-Replicator

Whenever you cast a historic spell, you may pay {1}. If you do, create a token that's a copy of Mishra's Self-Replicator. (Artifacts, legendaries, and Sagas are historic.)

Autonomous Assembler

Prototype {1}{W} — 2/2 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
Vigilance
{1}, {T}: Put a +1/+1 counter on target Assembly-Worker you control.

Urza's Mine

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