Sea serpent (Scooby-Doo! and the Legend of the Vampire)

The sea serpent was used as a fake monster by the Sea Serpent Smugglers

Physical appearance
It is a large serpentine creature with green scales, sharp teeth, and spikes.

Scooby-Doo! And The Legend Of The Vampire
While Mystery Inc. were pursued by the Kelp monster, Shark creature and the Peg leg captain, Shaggy Rogers accidentally slipped on a pail of water as he and Scooby-Doo landed in the pool. Then, a large sea serpent emerged and roared at them. Scooby accidentally popped it, thus revealing it to be a fake monster. When the three monsters were about to harm Fred Jones and the girls, the fake serpent landed right on the thieves.

Appearances

 * Scooby-Doo! And The Legend Of The Vampire