Activate Altar of Dementia by sacrificing River Kelpie.
When River Kelpie dies, its persist ability triggers, returning it from your graveyard to the battlefield without a -1/-1 counter on it due to Melira.
When River Kelpie enters, it triggers, causing you to draw a card
Resolve the Altar of Dementia ability.
Repeat.
This lovely little loop relies on Melira, Sylvok Outcast's static ability to bypass the traditional drawback of persist, ensuring River Kelpie returns to the battlefield completely free of the -1/-1 counters that would normally shut the mechanic down. By feeding River Kelpie into Altar of Dementia, you can sacrifice it repeatedly to mill your opponents out while triggering its own persist ability over and over. Every time River Kelpie re-enters the battlefield from the graveyard, its triggered ability fires off to draw you a card, turning your infinite sacrifice loop into a bottomless well of card draw.