When Wormfang Newt dies, its second ability triggers, returning a Plains from exile to the battlefield.
When the Plains enters the battlefield, Emeria Shepherd triggers.
Holding priority, activate the Plains by tapping it, adding .
Resolve the Emeria Shepherd trigger, returning Wormfang Newt from your graveyard to the battlefield.
When Wormfang Newt enters the battlefield, its first ability triggers, exiling a Plains.
Resolve the Shilgengar ability from step 1
Repeat.
This clever loop relies on Shilgengar, Sire of Famine as the sacrifice outlet that feeds our engine while generating a mountain of Blood tokens. Every time you feed Wormfang Newt to Shilgengar, its leaves-the-battlefield trigger returns an exiled Plains to the battlefield, which in turn triggers Emeria Shepherd's landfall ability to pull Wormfang Newt right back out of the graveyard. Because the Shepherd's triggered ability lets you drop the returning creature directly onto the battlefield when the land is a Plains, Wormfang Newt immediately re-enters and exiles that very same land again to keep the cycle going. Tapping the Plains for white mana before the landfall resolution lets you harvest infinite white mana alongside your endless sacrifice and ETB triggers.