Back in 2009, you could costumize as the Binary Bard. So you could copy it from somebody who did.
You can't costumize him.
Mordred does not appear as an interactive character, so it is apprently not possible to copy him.
Mordred is trapped in the far galaxy without any way to power his gateway. (Perhaps he will return?)
You can't "costumize" (copy) Mordred in the game, but you can find users in the multi-player room that have his "cyborg" face, and copy those.
With Mordred
go to the moon and there will be a building ask the owner wether you can costumize your space ship good luck
It is next to the Mordred Museum at the entrance to the island.
I think that it was Mordred.
Defeating Mordred and his warrior suit wins the island, and you receive the Island Medallion and 50 Poptropica credits.
You can't costumize him in Astro Knights Island or Super Villain Island but you might search the common rooms for someone with his face.
the museum in Astor knights island poptropica
When you defeat Mordred, the game is over, and the Princess will kayo him for you. (see the related question)