Pentavus dies, its persist ability triggers, returning it from your graveyard to the battlefield with four +1/+1 counters on it.
Activate
Pentavus' first ability twice by paying ({2} magic symbol) and removing two +1/+1 counters from it, creating two 1/1 Pentavite artifact creature tokens.
Activate
Clock of Omens by tapping
Pentavus and a Pentavite, untapping
Cauldron of Souls.
Repeat.
Once you have infinite colorless mana and Pentavite tokens, you may use
Pentavus' second ability to put infinite +1/+1 counters on it.