Dragon (animal)

Dragon is an animal in the series. It is a dragon, or a reptile of some sort, capable of flight.

Sennenryu (Filler Species)
A Sennenryu (千年竜, Thousand Year Dragon), known as a Millennium Dragon in the FUNimation dub, comes from Warship Island's mostly submerged Dragon's Nest. The only named one is Ryu.

They only appear in the anime only Warship Island Arc, and first appeared in Episode 55, but are also referenced in the Ocean's Dream arc.

Wano Dragon (Canon Species)
Oda had mixed the Monsters story to the One Piece main story. Hogback remarked that Ryuuma has slain a Dragon in Wano Country. However, Roronoa Zoro doubted the existence of dragons and that the samurai killed one.

Tashinoko Dragon (Filler & Game Species)
A dragon that appears in One Piece Dragon Dream game. It is the seahorse dragon.

This dragon also appears at the anime Ocean's Dream Arc which features it as the main villain who has the power to manipulate minds and memories and also has the power to cast illusions from the memories he gather. He somehow manipulates the mind of a young kid named Noko that somehow has the power of the Nemu Nemu no Mi that helps him to ease the memories of its victim faster.

Trivia

 * Richie dreamed about fighting a dragon in Buggy's Crew: After the Battle!
 * In Monster Time, Luffy was depicted as a dragon.