Scoobra Kadoobra - very spooky atmosphere, loved Maldor. That's Monstertainment - super creepy demon, great plot. Me and My Shadow Demon - the plot was cool, and gotta love the Shadow Demon! Ship of Ghouls - genuinely high-stakes/creepy situation, I just wish that the ghosts would have been in more than the last 7 minute of the episode! A Spooky Little Ghoul Like You - enjoyed Nicara as a villain
I have to go with It's a Wonderful Scoob for sure. It really shows how much Scooby means to everybody...and shows why Scooby keeps trying even when he feels like quitting. As long as his best friends and nephew remain alive he'll keep going...even if he's spooked out of his mind...just don't ever hurt Shaggy and Daphne or you'll really see what a mad dog looks like...as that makes Scrappy look nice by comparison.
After that, the classic mystery in the middle and circus episodes are my favorite.