Urza, Lord High Artificer + Corridor Monitor + Retraction Helix + Cloud Key

Urza, Lord High Artificer

Corridor Monitor

Retraction Helix

Cloud Key

How it works

1. Cast Retraction Helix by paying , targeting a creature you control that doesn't have summoning sickness.
2. Cast Corridor Monitor by paying due to Cloud Key.
3. When Corridor Monitor enters, it triggers, untapping the creature targeted by Retraction Helix.
4. Activate Urza's first ability by tapping Corridor Monitor, adding .
5. Activate the creature targeted by Retraction Helix by tapping it, returning Corridor Monitor from the battlefield to your hand.
6. Repeat from step 2.

This intricate loop transforms a simple creature bounce into a self-sustaining engine by weaving together mana generation and cost reduction. With Cloud Key set to artifacts, Corridor Monitor becomes free to recast, while Urza, Lord High Artificer serves as the crucial mana source by turning every newly entered automaton and construct into a Mox Sapphire. Retraction Helix grants the targeted creature the vital tapping ability needed to return Corridor Monitor to your hand immediately after it resolves, allowing you to replay it, trigger its untap ability, and repeat the cycle endlessly.