Ruthless Technomancer | Urza, Lord High Artificer | Cloudstone Curio

Cards

({4} magic symbol) ({U} magic symbol) ({U} magic symbol) ({B} magic symbol) plus up to an additional ({2} magic symbol) ({U} magic symbol) available.

Cast
Urza by paying ({2} magic symbol) ({U} magic symbol) ({U} magic symbol) .
When
Urza enters the battlefield, it and
Cloudstone Curio trigger.
Resolve the
Cloudstone Curio trigger, choosing to return
Ruthless Technomancer from the battlefield to your hand if its on the battlefield, or nothing otherwise.
Resolve the
Urza trigger, creating a 0/0 Construct artifact creature token.
Activate
Urza's first ability by tapping the Construct, adding ({U} magic symbol) .
Cast
Ruthless Technomancer by paying ({3} magic symbol) ({B} magic symbol) .
When
Ruthless Technomancer enters the battlefield, it and
Cloudstone Curio trigger.
Resolve the
Ruthless Technomancer trigger, causing you to sacrifice the Construct and create a number of Treasure tokens equal to its power.
Holding priority, activate
Urza's first ability by tapping a Treasure, adding ({U} magic symbol) .
Repeat step 9 until you have ({5} magic symbol) ({U} magic symbol) ({U} magic symbol) total available or until you have one untapped Treasure remaining.
Resolve the
Cloudstone Curio trigger, returning
Urza from the battlefield to your hand.
Activate a Treasure by tapping and sacrificing it, adding ({B} magic symbol) .
Repeat.

The additional mana cost may be waived or reduced depending on how many artifacts you control as you start the combo. You can also use artifacts you control to tap them via
Urza's first ability, reducing the possible cost down to ({2} magic symbol) ({U} magic symbol) ({U} magic symbol) ({B} magic symbol) .
Once you have infinite mana, you may use it to activate
Urza's ability.