After Joker was defeated by Tatsuya Suou and his party in the Caracol, he is possessed by his Persona Joker-Nyarlathotep, who says that since people view him as an angel, he shall make him such. After Angel Joker was defeated, Joker was unmasked as Jun Kurosu and stripped of his Persona by Nyarlathotep.
Earlier in the game, a civilian who was protected from the Last Battalion by the Masked Circle referred to Joker as an angel, while a beaten Masked Circle member cursed him as a devil. Originally, this would result in a rumor that the player would spread about Joker's "true form", but the option was removed from the final version of the game. The alternate second form was to be called Devil Joker.
Even though the battle against Angel Joker follows right after the previous fight against Joker's original form, the whole party's HP and SP is automatically recovered, except for status ailments. If the player made the correct dialogue choice at the entrance of Caracol, Yukino will rejoin the team for this battle one last time (and replaced by Jun afterwards).
Angel Joker relies on three Light skills which can be negated by Tetraja or a Silver Manisha, or just have the whole team equip Personas with Light immunity. Since he is weak to non-fatal Darkness attack, Stagnant Air actually works on him, unlike most circumstances.
Joker has an unused animation turning into Devil Joker, only currently viewable in Unit Viewer. The cutscene for this sprite supposed to appear in is currently unknown.
Depsite being dummied out, Devil Joker has a complete stats line, contact and spell list. The two unique skills that would be used by him are Chaos Element and Perishable Darkness. These skills wouldn't be used till the sequel, Eternal Punishment.
Devil Joker’s lines and dialogue have been fully translated in the US/PAL release for the PSP version.
Ginko, Eikichi and Maya have unused dialogue for the Devil Joker fight. Eikichi comments on what happened to Joker in confusion as Maya begs Jun to stop this. Ginko asks Tatusya if it's too late to save Jun.