Lands you control can tap to produce at least ({8} magic symbol) ({U} magic symbol) ({U} magic symbol) .
Steps
Activate Liquimetal Torque's second ability by tapping it, causing Mnemonic Wall to become an artifact until end of turn.
Activate all mana-producing lands you control by tapping them, adding at least ({8} magic symbol) ({U} magic symbol) ({U} magic symbol) .
Cast Turnabout by paying ({2} magic symbol) ({U} magic symbol) ({U} magic symbol) , untapping all lands you control.
Activate Urza by paying ({6} magic symbol) , creating a token copy of Mnemonic Wall that is a 1/1 Soldier in addition to its other types.
When the Mnemonic Wall token enters the battlefield, it triggers, returning Turnabout to your hand from your graveyard.
Repeat from step 2.
If lands you control can tap to proudce at least ({9} magic symbol) ({U} magic symbol) ({U} magic symbol) , this combo nets infinite mana, which can be used to activate Urza's ability infinitely and/or cast Turnabout choosing its other modes.
Results
Infinite creature copies of artifacts you control.