Wilf, along with Rachel, Marv, Hank and Sarah, may be encountered during Temple Trekking. The challenge involves quickly feeding them. If Wilf is left without food for too long he begins to resemble a ghast before eventually turning into one. If this happens, the ghast must be killed.
He can be fed almost any normal cooked food, but in case the player does not have any food, then the nearby snails can be killed and cooked for him to eat.
High level followers will help with this by starting a fire.