When Casper's been being friendly lately even when playing with a boy named Jimmy, Kibosh: The King of the Underworld has Casper enrolled into a Scare School headed by the two-headed headmaster Alder and Dash. He befriends Ra, a mummy with unraveling issues and Mantha, a zombie girl who keeps falling apart. When Casper discovers the two-headed headmaster's plot to use a petrification potion to turn Kibosh into stone and take over the Underworld and Deedstown, he and his new friends must stop him.
The second best follow-up to 'Casper', so... yeah.
'Caspers Scare School' arguably has the best plot of the four prequels/sequels, but remains hampered by the very poor animation - which, even for 2006, looks awful. I did recognise a few of the voices, including Kevin McDonald (aka Pleakley) and John DiMaggio (aka Bender). All in all, though, it's another pointless production - and, thankfully, the last... at time of review, at least.
