Activate Ashnod's Altar by sacrificing Breya's Apprentice, adding {C}{C}.
When Breya's Apprentice dies, Nim Deathmantle triggers, causing you to pay {4} to return Breya's Apprentice from your graveyard to the battlefield and attach Nim Deathmantle to it.
When Breya's Apprentice enters, it triggers, creating a creature token.
Activate Ashnod's Altar by sacrificing a creature token, adding {C}{C}.
Repeat.

Infinite death triggers

Infinite ETB

Infinite LTB

Infinite sacrifice triggers

Nim Deathmantle

Ashnod's Altar

Breya's Apprentice

Activate Krark-Clan Ironworks by sacrificing Breya's Apprentice, adding {C}{C}.
Breya's Apprentice dies, triggering Nim Deathmantle, causing you to pay {4} to return Breya's Apprentice from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Breya's Apprentice enters the battlefield, creating a 1/1 Thopter artifact creature token.
Activate Krark-Clan Ironworks by sacrificing the Thopter, adding {C}{C}.
Repeat.

Krark-Clan Ironworks

Activate Breya's Apprentice by tapping it and sacrificing Lesser Masticore.
When Lesser Masticore dies, its persist ability and Dross Scorpion trigger.
Resolve the Dross Scorpion trigger, untapping Breya's Apprentice.
Resolve the Lesser Masticore trigger, returning it from your graveyard to the battlefield with no -1/-1 counters on it due to Vizier of Remedies.
Resolve the Breya's Apprentice ability, either giving target creature +2/+0 until end of turn, or exiling the top card of your library with the ability to play it until the end of your next turn.
Repeat.

Combos with "Breya's Apprentice"