Activate Feldon of the Third Path by paying {2}{R} and tapping it, creating a token copy of Diamond Lion with haste.
Activate Diamond Lion by tapping it, discarding your hand, and sacrificing it, adding {R}{R}{R}.
Thornbite Staff and Stalking Vengeance both trigger.
Resolve the Stalking Vengeance trigger, dealing damage equal to Diamond Lion's power to any target.
Resolve the Thornbite Staff trigger, untapping Feldon of the Third Path.
Repeat.

Infinite damage

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite creature sacrifice triggers

Feldon of the Third Path

Diamond Lion

Thornbite Staff

Stalking Vengeance

Activate Dalakos by tapping it, adding {C}{C} that can only be spent on artifacts or to activate abilities of artifacts.
Activate Pentavus's first ability by paying {1}, creating a 1/1 Pentavite creature token.
Creature tokens enters the battlefield, triggering Intruder Alarm, untapping all creatures.
Activate Pentavus's second ability by paying {1} and sacrificing a Pentavite, putting a +1/+1 counter on Pentavus.
Stalking Vengence triggers, dealing 1 damage to any target.
Repeat.

Infinite artifact ETB

Infinite artifact LTB

Infinite artifact sacrifice triggers

Infinite mana creatures you control can produce

Infinite untap of creatures

Dalakos, Crafter of Wonders

Pentavus

Intruder Alarm

Activate Dalakos by tapping it, adding {C}{C} that can only be spent on artifacts or to activate abilities of artifacts.
Activate Pentavus's first ability by paying {1}, creating a 1/1 Pentavite creature token.
Activate Pentavus's second ability by paying {1} and sacrificing a Pentavite, putting a +1/+1 counter on Pentavus.
Dalakos triggers, untapping.
Stalking Vengeance triggers, dealing 1 damage to any target.
Repeat.

Combos with "Stalking Vengeance"