Hammerhand appeared as a dead spirit who took possession of the cloned body of Panthro. But he previously appeared in The Terror of Hammerhand as a living person and would later appear again as a living person in season 2.
Goof: When the Driller knocked Panthro out and pulled him into the tunnel he dug to take him to Mumm-Ra, Panthro was wearing nothing except the belt and boots he wore in Exodus before being clothed by Jaga. But in the following scene as he laid unconscious before Mumm-Ra, he was fully dressed in his ThunderCat clothes.
Cheetara: Hey, imagine what would happen if one of us really did turn bad.
Panthro: We just have to make sure we never do.
Tygra: That's right, Panthro. The ThunderCat power gives us extra responsibility.
Lion-O: One thing's for sure. (to Panthro) I'm glad you're one of the good guys.
Lion-O: How can I help you, Panthro? I can't tell the real you from the fake.
Snarf: The sword, Lion-O! Use the sword!
Lion-O: Not against a ThunderCat, Snarf! Our code expressly forbids it!
Snarf: Exactly! The sword will only harm the fake ThunderCat!
(Believing he's facing the real Panthro)
Lion-O: Panthro! Stop! You don't know what you're doing!
Panthro Clone: Frightened, cub?
Lion-O: You're not yourself! Don't force me to fight you, Panthro. Jaga forbade us to fight amongst ourselves.
Panthro Clone: Jaga is gone, cub. Now I serve a new master.
Lion-O: Whatever caused it, we will help repair the damage.
Wollo: I'm sorry, Lion-O. None of us will ever trust you again.
First Appearance: Driller.