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 Vizier of Remedies.
When River Kelpie enters, its first ability triggers, causing you to draw a card.
Resolve the Shilgengar ability.
Repeat.
This clever loop relies on Shilgengar, Sire of Famine to repeatedly sacrifice River Kelpie, which triggers the latter's persist ability to bring itself right back from the graveyard. Normally, persist would saddle River Kelpie with a -1/-1 counter and shut down future returns, but Vizier of Remedies steps in to cleanly reduce that counter placement to zero. Every time River Kelpie re-enters the battlefield from the graveyard, its first ability triggers to draw you a card while Shilgengar, Sire of Famine simultaneously generates a Blood token for the sacrifice, giving you an endless cycle of resources.