Cast Roxanne either from your hand or from the command zone by paying {3}{R}{G} plus commander tax, if applicable.
When Roxanne enters the battlefield, its first ability triggers twice.
Resolve the first trigger, creating a Meteorite artifact token.
When the Meteorite enters the battlefield, it and Amulet of Vigor trigger twice.
Resolve both Meteorite triggers, dealing 4 damage to any target.
Resolve the first Amulet of Vigor trigger, untapping the Meteorite.
Activate the Meteorite by tapping it, adding {R/G}.
Roxanne's second ability triggers, adding {R/G}.
Repeat from step 6 for the remaining Amulet of Vigor trigger.
Repeat from step 3 for the remaining Roxanne trigger.
Activate Temur Sabertooth by paying {1}{G}, returning Roxanne from the battlefield to your hand.
Repeat.
Once you have infinite mana, you may forego tapping the Meteorites for mana and/or add mana of any color(s).

Infinite colored mana

Infinite damage

Infinite ETB

Infinite LTB

Infinite Meteorite tokens

Infinite storm count

Infinite blinking

Roxanne, Starfall Savant

Amulet of Vigor

Panharmonicon

Temur Sabertooth

Cast Rootcast Apprenticeship by paying {3}{G}. Choose its second mode three times targeting the Meteorite.
Holding priority, cast Reiterate with buyback by paying {4}{R}{R}, copying Rootcast Apprenticeship, targeting the Meteorite with all three modes, and returning Reiterate to your hand.
Resolve the Rootcast Apprenticeship copy, creating three copies of the Meteorite token. 
When the Meteorites enter, they trigger, dealing 6 damage to any target.
Activate the three Meteorites by tapping them, adding {2}{R}.
Roxanne triggers three times, adding {2}{R}.
Repeat from step 2.

Infinite magecraft triggers

Infinite tapped Meteorite tokens

Reiterate

Rootcast Apprenticeship

Activate Svella's first ability by paying {1} and tapping it, creating a Icy Manalith token.
Activate the Icy Manalith token by tapping it, adding {1}.
Roxanne's second ability triggers, adding {1}.
Activate Svella by paying {1} and untapping it, giving it +2/+2 until end of turn.
Repeat.

Infinitely large creature until end of turn

Infinite tapped Icy Manalith tokens

Svella, Ice Shaper

Agatha of the Vile Cauldron

Umbral Mantle

Cast Molten Duplication by paying {1}{R}, 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.

Infinite colorless mana

Basalt Monolith

Molten Duplication

Activate Roxanne by paying {1}{U}, blinking it.
When Roxanne enters, its first ability and Deadeye Navigator's soulbond ability trigger.
Resolve the Deadeye Navigator trigger, repairing it and Roxanne.
Resolve the Roxanne trigger, creating a tapped Meteorite token.
When the Meteorite enters, it and Amulet of Vigor trigger.
Resolve the Meteorite trigger, dealing 2 damage to any target.
Resolve the Amulet of Vigor trigger, untapping the Meteorite.
Activate the Meteorite by tapping it, adding {U}.
Roxanne's second ability triggers, adding {U}.
Repeat.

Deadeye Navigator

Combos with "Roxanne, Starfall Savant"