Activate Adarkar Valkyrie by tapping it, targeting any legendary creature you control.
Cast Protean Raider by paying {1}{U}{R}, choosing to have it enter the battlefield as a copy of the legendary creature targeted in step 1.
Put the legendary creature into your graveyard due to the legend rule.
Adarkar Valkyrie and Intruder Alarm trigger.
Resolve the Intruder Alarm trigger, untapping all creatures.
Holding priority, activate Adarkar Valkyrie by tapping it, targeting Protean Raider.
Resolve the Adarkar Valkyrie trigger from step 4, returning the legendary creature to the battlefield from your graveyard.
Put Protean Raider into your graveyard due to the legend rule.
Adarkar Valkyrie and Intruder Alarm trigger.
Resolve the Intruder Alarm trigger, untapping all creatures.
Holding priority, activate Adarkar Valkyrie by tapping it, targeting the legendary creature.
Resolve the Adarkar Valkyrie trigger from step 9, returning Protean Raider to the battlefield from your graveyard as a copy of the legendary creature.
Repeat from step 3.

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite mana creatures you control can produce

Infinite untap of creatures

Adarkar Valkyrie

Intruder Alarm

Protean Raider

Cast Protean Raider by paying {1}{U}{R}, choosing to have it enter the battlefield as a copy of Swift Warkite.
When Protean Raider enters the battlefield, it triggers.
Holding priority, activate Ashnod's Altar by sacrificing Protean Raider, adding {C}{C}.
Resolve the Protean Raider trigger, returning Protean Raider from your graveyard to the battlefield as a copy of Swift Warkite.
Repeat from step 2.

Infinite colorless mana

Infinite creature sacrifice triggers

Swift Warkite

Ashnod's Altar

Activate Phyrexian Altar by sacrificing Protean Raider, adding {B}.
When Protean Raider dies, it triggers, causing you to mill six cards and return Unearth and up to one other instant or sorcery card from your graveyard to your hand.
Cast Unearth by paying {B}, returning Protean Raider from your graveyard to the battlefield as a copy of Kairi.
Repeat.

Combos with "Protean Raider"