Activate Ashnod's Altar by sacrificing Infernal Vessel, adding {C}{C}.
When Infernal Vessel dies, it triggers, returning itself from your graveyard to the battlefield as a Demon in addition to its other types.
Activate Ashnod's Altar by sacrificing Infernal Vessel, adding {C}{C}.
When Infernal Vessel dies, Valkyrie's Call triggers, returning Infernal Vessel from your graveyard to the battlefield as an Angel in additional to its other types.
Repeat.

Infinite LTB

Infinite ETB

Infinite sacrifice triggers

Infinite death triggers

Infinite colorless mana

Infernal Vessel

Valkyrie's Call

Ashnod's Altar

Activate Ashnod's Altar by sacrificing Optimus Prime, Hero, adding {C}{C}.
When Optimus Prime, Hero dies, its second ability triggers, returning it from your graveyard to the battlefield as Optimus Prime, Autobot Leader.
Activate Ashnod's Altar by sacrificing Optimus Prime, Autobot Leader, adding {C}{C}.
When Optimus Prime, Autobot Leader dies, Valkyrie's Call triggers, returning Optimus Prime from your graveyard to the battlefield as Optimus Prime, Hero as an Angel with flying.
Repeat.

Optimus Prime, Hero // Optimus Prime, Autobot Leader

Cast the Vehicle by paying its mana cost.
When the Vehicle enters the battlefield, Simulacrum Synthesizer triggers, creating a 0/0 Construct artifact creature token that gets +1/+1 for each artifact you control.
Activate the Vehicle's crew ability by tapping the Construct, causing the Vehicle to become an artifact creature until end of turn.
Activate Ashnod's Altar by sacrificing the Vehicle.
When the Vehicle dies, Valkyrie's Call triggers, returning the Vehicle from your graveyard to the battlefield. It will not be an Angel because the Vehicle is no longer a creature and cannot gain creature types.
When the Vehicle enters the battlefield, Simulacrum Synthesizer triggers, creating a 0/0 Construct artifact creature token that gets +1/+1 for each artifact you control.
Repeat from step 3.

Infinite tapped creature tokens

Vehicle with MV >= 3 and a Crew Ability

Simulacrum Synthesizer

Activate Shilgengar by sacrificing Felidar Guardian.
When Felidar Guardian dies, Valkyrie's Call triggers, returning Felidar Guardian from your graveyard to the battlefield as an Angel.
When Felidar Guardian enters the battlefield, it triggers, blinking Conspiracy. Choose any creature type except "Angel" as Conspiracy enters the battlefield.
Resolve the Shilgengar ability.
Repeat.

Felidar Guardian

Conspiracy

Shilgengar, Sire of Famine

Activate Kiki-Jiki by tapping it, creating a token copy of Ruthless Technomancer with haste.
When the Ruthless Technomancer token enters the battlefield, it triggers, causing you to sacrifice Kiki-Jiki and create two Treasure tokens,
When Kiki-Jiki dies, Valkyrie's Call triggers, returning Kiki-Jiki from your graveyard to the battlefield as an Angel with flying and a +1/+1 counter on it.
Activate Kiki-Jiki by tapping it, creating a token copy of Ruthless Technomancer with haste.
When the Ruthless Technomancer token enters the battlefield, it triggers, causing you to sacrifice Kiki-Jiki and create three Treasure tokens,
Activate thee Treasure tokens by tapping and sacrificing them, adding {2}{B}.
Activate a Ruthless Technomancer by paying {2}{B} and sacrificing two Treasures, returning Kiki-Jiki from your graveyard to the battlefield.
Repeat.

Infinite creature tokens with haste

Kiki-Jiki, Mirror Breaker

Ruthless Technomancer

Activate Amoeboid Changeling's second ability by tapping it, causing another nontoken creature you control to lose all creature types until end of turn.
Activate Phyrexian Altar by sacrificing the creature targeted in step 1, adding one mana of any color.
When the creature dies, Valkyrie's Call triggers, returning the creature from your graveyard to the battlefield as a white Angel.
When the creature enters the battlefield, Intruder Alarm triggers, untapping all creatures.
Repeat.

Combos with "Valkyrie's Call"