Cast Three Steps Ahead by paying {3}{U}, creating a token copy of Worldwalker Helm and a Map token.
Activate Urza's first ability by tapping a Worldwaker Helm and a Map, adding {U}{U}.
Activate a Worldwalker Helm by paying {1}{U} and tapping it, creating a token copy of the Worldwalker Helm token and two Map tokens.
Activate Urza's first ability twice by tapping the Maps, adding {U}{U}.
Repeat from step 3.

Infinite tapped Map tokens

Urza, Lord High Artificer

Worldwalker Helm

Three Steps Ahead

Cast Three Steps Ahead by paying {3}{U}, creating a token copy of Basalt Monolith.
Activate the token Basalt Monolith's first ability by tapping it, adding {C}{C}{C}.
Roxanne's second ability triggers, adding {C}.
Activate the token Basalt Monolith's second ability by paying {3}, untapping it.
Repeat from step 2.

Combos with "Three Steps Ahead"