When Rhys enters, it triggers, giving Reveillark persist until end of turn.
Activate Viscera Seer by sacrificing Rhys.
Activate Viscera Seer by sacrificing Reveillark.
When Reveillark dies, its ability and its persist ability trigger.
Resolve the persist trigger, returning Reveillark from your graveyard to the battlefield without a -1/-1 counter on it due to Solemnity.
Resolve the second trigger, returning Rhys from your graveyard to the battlefield.
When Rhys enters, it triggers, giving Reveillark persist until end of turn.
Resolve the Viscera Seer ability from step 4.
Repeat from step 3.
This resilient loop relies on Viscera Seer to cleanly sacrifice your creatures while generating endless scry utility, fueling the engine with every iteration. The key to bypassing normal mechanical limits is Solemnity, whose passive enchantment effect stops -1/-1 counters from ever being placed on creatures. Because of this, when Rhys, the Evermore grants persist to Reveillark and the latter is sent to the graveyard, it returns completely free of counters to trigger its own graveyard-recursion ability. Reveillark then brings back Rhys, which immediately refreshes the persist grant upon re-entry, allowing you to repeat this sacrifice-and-return cycle indefinitely.