Activate Shilgengar by sacrificing Ruthless Ripper
When Ruthless Ripper dies, Yedora triggers, returning Ruthless Ripper from your graveyard to the battlefield face down as a Forest land.
Resolve the Shilgengar ability
Activate Ruthless Ripper's morph ability by revealing a black card from your hand, turning it face up.
Repeat.
This intricate loop lets you bleed your opponents dry by continuously recycling a single creature into the earth and back again. Shilgengar, Sire of Famine acts as the engine, sacrificing Ruthless Ripper to generate a Blood token while sending the Ripper to the graveyard. That death triggers Yedora, Grave Gardener, which immediately rescues the Ripper from the yard and plants it right back onto the battlefield face down as a fresh Forest land. From there, you simply use Ruthless Ripper's morph ability to turn it face up, draining life away before feeding it back to Shilgengar to start the whole cycle anew.