Sea Dragons are not Dragons at all, they are over-sized Sea Horses. In FFA they lived underwater and never left the sea, but from SD3 and beyond they have been hopping around on dry land.
These monsters live in almost every ocean scene in FFA. They pop up and down in the sea and will shoot fireballs at your character. There is a small island located in the middle of the ocean where killing all of the surrounding Sea Dragons will gain you an Elixir.
In SD3 Sea Dragons are classified as Fish.
Sea Serpents are located in the Sub-Zero Snowfields. They are one of the most simple enemies in the game and only possess a pouncing attack.
These pumped up Sea Serpents live in the Labyrinth of Ice Walls and have gained a more powerful double pounce as well as a Chilly Breath attack. Their Chilly Breath move is only used on low life and will freeze one character.
In LoM Sea Dragons are classified as Aquatic.
Sea Dragons live on Madora Beach, the S.S. Buccaneer and in the Fieg Snowfields. They attack with flips and their icy cold breath. As a pet they will add a freezing effect to your attacks.