Let's say I have a Doomed Dissenter on the battlefield.
When Doomed Dissenter dies, create a 2/2 black Zombie creature token.
Then I play Lord of Tresserhorn.
When Lord of Tresserhorn enters the battlefield, you lose 2 life, you sacrifice two creatures, and target opponent draws two cards.
For the two creatures I must sacrifice, can I choose Doomed Dissenter, and then the Zombie token it creates? Do I need to choose two creatures that are on the battlefield before either one dies?