User blog comment:Yoshifan996/Garmadon, Morro, Ghost Warriors, Andacondrai Cultists and Chen's fates/@comment-27507964-20160131014229/@comment-27507964-20160201033221

His father hadn't died when he was sent to the cursed realm. Mortal bodies cannot travel into the cursed realm so their bodies float around as little particles until they come back. (The spell the cultists used summoned the parts of the anacondrai generals who were banished. This was all revealed on the Ninjago website.) So Garmadon was a ghost, like Cole, who could not die. When the preeminent came into Ninjago Garmadon's little parts found him again and he was able to die, sending him to one of the better afterlives.