Activate Shilgengar by sacrificing another nontoken green Insect.
When the Insect dies, Zask and Verdant Succession trigger.
Resolve the Zask trigger, putting the Insect on the bottom of your library from your graveyard and causing you to mill two cards.
Resolve the Verdant Succession trigger, searching your library for that Insect and putting it onto the battlefield.
Resolve the Shilgengar ability.
Repeat.
This crafty loop turns the graveyard into a revolving door for your bugs, anchored by Shilgengar, Sire of Famine and his appetite for sacrifice. Whenever you feed a green Insect to Shilgengar, Verdant Succession steps in to immediately fetch a fresh copy of that creature straight from your library onto the battlefield. Meanwhile, Zask, Skittering Swarmlord catches the fallen bug as it dies, recycling it to the bottom of your library while fueling your graveyard with fresh mills—all while Shilgengar keeps cranking out Blood tokens to fund your future resurrections.