The Hairy Scare of the Devil Bear - S1-E8
Character mistake: Velma says bears only have four claws. Wrong, they really do have five claws.
Scooby-Doo and Scrappy-Doo (1979)
1 character mistake in season 1
Starring: Don Messick, Casey Kasem, Lennie Weinrib, Heather North
Other mistake: When Scooby is eating the hot dogs at the "Hotus Dogus" stand, his tail goes transparent.