Activate Ashnod's Altar by sacrificing Syrix, adding {C}{C}.
Choose not to move Syrix from your graveyard to the command zone.
Syrix dies, triggering Pitiless Plunderer, creating a Treasure token.
Activate Ashnod's Altar by sacrificing Skyfire Phoenix, adding {C}{C}.
Skyfire Phoenix dies, triggering Syrix and Pitiless Plunderer.
Resolve the Pitiless Plunderer trigger, creating a Treasure token.
Activate both Treasure tokens by tapping and sacrificing them, adding {B}{R}.
Resolve the Syrix trigger, causing you to pay {2}{B}{R} to cast Syrix from your graveyard.
Skyfire Phoenix triggers, returning itself from your graveyard to the battlefield.
Repeat.

Infinite colorless mana

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite creature sacrifice triggers

Syrix, Carrier of the Flame

Skyfire Phoenix

Ashnod's Altar

Pitiless Plunderer

Activate Phyrexian Altar by sacrificing Syrix, adding {1}.
Choose not to move Syrix from your graveyard to the command zone.
Syrix dies, triggering Pitiless Plunderer, creating a Treasure token.
Activate Phyrexian Altar by sacrificing Skyfire Phoenix, adding {1}.
Skyfire Phoenix dies, triggering Syrix and Pitiless Plunderer.
Resolve the Pitiless Plunderer trigger, creating a Treasure token.
Activate both Treasure tokens by tapping and sacrificing them, adding {B}{R}.
Resolve the Syrix trigger, causing you to pay {2}{B}{R} to cast Syrix from your graveyard.
Skyfire Phoenix triggers, returning itself from your graveyard to the battlefield.
Repeat.

Phyrexian Altar

Activate Ashnod's Altar by sacrificing Syrix, adding {2}.
Choose not to move Syrix from your graveyard to the command zone.
Activate Ashnod's Altar by sacrificing Skyfire Phoenix, adding {2}.
Skyfire Phoenix dies, triggering Syrix, causing you to pay {4} to cast Syrix from your graveyard.
Skyfire Phoenix triggers, returning itself from your graveyard to the battlefield.
Repeat.

Infinite card draw

Infinite colored mana

Infinite draw triggers

Chromatic Orrery

Mycosynth Lattice

Activate Paradise Mantle's equip ability by paying {1}, attaching it to Syrix.
Activate Syrix by tapping it, adding {B}.
Activate Paradise Mantle's equip ability by paying {1}, attaching it to Skyfire Phoenix.
Activate Skyfire Phoenix by tapping it, adding {R}.
Activate Ashnod's Altar by sacrificing Syrix, adding {C}{C}.
Choose not to move Syrix from your graveyard to the command zone.
Activate Ashnod's Altar by sacrificing Skyfire Phoenix, adding {C}{C}.
Skyfire Phoenix dies, triggering Syrix, causing you to pay {2}{B}{R} to cast Syrix from your graveyard.
Skyfire Phoenix triggers, returning itself from your graveyard to the battlefield.
Repeat.

Paradise Mantle

Combos with "Syrix, Carrier of the Flame"