I have a question about Tyrannosaurus Zombie: Greater Undead from Tomb of Annihilation, whose ability reads: "When fielded, you may purchase a Zombie character die for free and immediately field it at level 2."
My question is as follows: What constitutes a "Zombie" character die for the purposes of this effect?
1) A character with "Zombie" in their name, including other copies of Tyrannosaurus Zombie.
2) A character whose name is only "Zombie".
3) A character with the "Zombie" affiliation from the 1-die super rares from Age of Ultron and Amazing Spider-man.
Thank you for your time.