Activate Ashnod's Altar by sacrificing another nontoken nonartifact creature, adding {C}{C}.
When the creature dies, Missy's first ability and Pitiless Plunderer trigger.
Resolve the Missy trigger, returning the creature from your graveyard to the battlefield face down as a 2/2 Cyberman artifact creature.
Resolve the Pitiless Plunderer trigger, creating a Treasure artifact token.
Activate the Treasure by tapping and sacrificing it, adding {U}.
Activate Ixidor by paying {2}{U}, turning the creature face up.
Repeat.

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite creature sacrifice triggers

Missy

Ixidor, Reality Sculptor

Pitiless Plunderer

Ashnod's Altar

Activate Isochron Scepter by paying {2} and tapping it, casting a copy of Backslide without paying its mana cost.
Resolve Backslide, turning Brine Elemental face down.
Activate Ixidor by paying {2}{U}, turning Brine Elemental face up.
Brine Elemental triggers, causing each opponent to skip their next untap step.
Repeat during each of your turns.

Opponents skip their untap steps

Lock

Brine Elemental

Isochron Scepter

Backslide

Activate Phyrexian Altar by sacrificing Ashcloud Phoenix, adding {U}.
When Ashcloud Phoenix dies, it triggers, returning itself from your graveyard to the battlefield face-down.
Activate Ixidor by paying {U}, turning Ashcloud Phoenix face up.
Repeat.

Combos with "Ixidor, Reality Sculptor"