When Ulasht dies, its persist ability triggers, returning it from your graveyard to the battlefield without a -1/-1 counter on it due to its replacement effect.
Resolve the Woe Strider ability.
Repeat.
This loop turns the night side of Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight into an engine of endless resurrection, granting persist to Ulasht, the Hate Seed so it keeps coming back from the graveyard. Woe Strider acts as the sacrificial outlet that triggers this recursive cycle, while simultaneously allowing you to filter your draws with its scry ability. Because Ulasht returns without a -1/-1 counter due to how persist interacts with its counters, you can feed it to the Strider over and over again to generate infinite sacrifice, entry, and death triggers.