Activate Woe Strider by sacrificing Pyreheart Wolf
When Pyreheart Wolf dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Resolve the Woe Strider ability.
Activate Woe Strider by sacrificing Pyreheart Wolf
When Pyreheart Wolf dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
Pyreheart Wolf enters and dies as a state-based action due to having 0 toughness. Its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Resolve the Woe Strider ability from step 4.
Repeat from step 4.
This clever loop is anchored by Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight, whose backside grants persistent staying power by giving your other nontoken creatures persist. By feeding creatures to Woe Strider's sacrifice outlet, you trigger a clever counter-neutralizing dance: when Pyreheart Wolf dies with a +1/+1 counter from its own undying ability, Isilu's newly granted persist brings it back with a -1/-1 counter, which immediately annihilates both counters as a state-based action. This resets the wolf so its own undying triggers all over again, generating an endless cascade of sacrifices, enters-the-battlefield triggers, and smooth scrys.