The entire Mystery, Inc. gang returns from the first movie including Fred (Freddie Prinze, Jr.), Daphne (Sarah Michelle Gellar), Velma (Linda Cardellini), Shaggy (Matthew Lillard) and of course Scooby-Doo himself.
http://www.ign.com/articles/2004/03/25/review-of-scooby-doo-2-monsters-unleashed
Daphne believes Jonathan Jacobo, the original Pterodactyl Ghost is the culprit, but Velma reveals he died after a prison escape. The gang then decide that Jeremiah Wickles, the Black Knight Ghost, is behind the mystery and set out to his mansion.
http://scoobydoo.wikia.com/wiki/Scooby-Doo_2:_Monsters_Unleashed
On July 8, 2015, it was announced that Kate Micucci would take over the role of Velma in the upcoming series Be Cool, Scooby-Doo!, with Cohn continuing to provide her voice for future direct-to-DVD movies and games. In the 2002 and 2004 live-action movies, Velma is played by Linda Cardellini. Velma is portrayed by Hayley Kiyoko in the 2009 live-action movie Scooby-Doo! The Mystery Begins and its live-action sequel Scooby-Doo! Curse of the Lake Monster.
https://en.wikipedia.org/wiki/Velma_Dinkley
The five then find a hidden room that has a giant machine in it. Velma figures that Patrick is the culprit. Fred, Daphne and Velma go to explore the rest of the caves nearby, leaving Shaggy and Scooby with the machine. The two find a control panel and unknowingly activate the machine, bringing more monsters to life.
http://scoobydoo.wikia.com/wiki/Scooby-Doo_2:_Monsters_Unleashed
Scooby-Doo 2: Monsters Unleashed is a blast to watch. It doesn't break any new ground and it's far from a masterwork, but it works incredibly well as pure entertainment. It's fun to watch and, at times, pretty amusing.
http://www.ign.com/articles/2004/03/25/review-of-scooby-doo-2-monsters-unleashed
Scooby-Doo, Shaggy, Velma, Daphne and Fred of Mystery Inc., are now celebrities in their hometown of Coolsville, after previously solving the mystery on Spooky Island. The gang are attending the grand opening of the Coolsonian Criminology Museum as the guests of honor and greeted by their screaming fans.
http://scoobydoo.wikia.com/wiki/Scooby-Doo_2:_Monsters_Unleashed
While I must admit that I did enjoy the original on some level, Scooby-Doo 2 is a huge improvement. If you couldn't get past the live-action aspect of the first film, you'll likely still have that problem here. Nevertheless, Scooby Doo 2: Monsters Unleashed should please Scooby fans willing to overlook that aspect. While the the first movie took place on an island and had a very elaborate plot involving both Scrappy-Doo and Mr. Bean, the sequel is much more loyal to the feel and fun of the original show.
http://www.ign.com/articles/2004/03/25/review-of-scooby-doo-2-monsters-unleashed
Velma Dinkley is a fictional character in the Scooby-Doo franchise. She is prone to losing her glasses. She is usually seen wearing a baggy orange turtleneck, short pleated skirt (or in later episodes an A-line skirt, or sometimes shorts), knee socks, and Mary Janes. She is seen as the brains of the group.
https://en.wikipedia.org/wiki/Velma_Dinkley
1 Redbeard's Ghost: One of the monsters that was to appear in the film, but was scrapped and replaced by Miner 49er, although his costume, ghost ship and portrayer, C.L. Magnus, appeared, played by Stephen E. Miller.  Creeper: The Creeper is a zombie that was replaced by the Zombie in the film. He can walk through walls.
http://scoobydoo.wikia.com/wiki/Scooby-Doo_2:_Monsters_Unleashed
In Scooby-Doo! Abracadabra-Doo, Velma is described by her younger sister Madelyn as being born with a mystery book in her hand. Consequently, Velma is usually the one to figure out the mystery, sometimes with the help of Fred and Daphne.
https://en.wikipedia.org/wiki/Velma_Dinkley
who plays velma in scooby doo 2
Linda Cardellini plays Velma in Scooby-Doo 2. Linda Cardellini plays Velma in Scooby Doo 2.