Urza, Lord High Artificer + Deadeye Navigator + Panharmonicon

Urza, Lord High Artificer

Deadeye Navigator

Panharmonicon

How it works

1. Activate Urza by paying 1, blinking it.
2. When Urza enters the battlefield, it and Deadeye Navigator's soulbond ability trigger twice.
3. Resolve both Deadeye Navigator triggers, repairing it and Urza.
4. Resolve both Urza triggers, creating two 0/0 Construct artifact creature tokens.
5. Activate Urza's first ability twice by tapping the Constructs, adding .
6. Repeat.

This loop hinges on Urza, Lord High Artificer and Deadeye Navigator being soulbonded so that Urza can repeatedly exile and return itself to the battlefield. Normally, a single blink would just net you one Construct token from Urza's enter-the-battlefield trigger, but Panharmonicon doubles that trigger, causing two Construct artifact creature tokens to appear instead of one. Those newly minted tokens can immediately be tapped for blue mana using Urza's built-in mana ability, easily funding the {1}{U} cost required by Deadeye Navigator to keep the chain going indefinitely.