Vaporeon

Red +2: Lives close to water. Its long tail is ridged with a fin which is often mistaken for a mermaid's.

Yellow: Its cell structure is similar to water molecules. It will melt away and become invis­ ible in water.

Gold: When VAPOREON's fins begin to vi­ brate, it is a sign that rain will come within a few hours.

Silver: It prefers beauti­ ful shores. With cells similar to water molecules, it could melt in water.

Crystal: As it uses the fins on the tip of its tail to swim, it blends with the water perfectly.

Ruby / Sapphire: VAPOREON underwent a spontaneous mutation and grew fins and gills that allow it to live underwater. This POKéMON has the ability to freely control water.

Emerald: VAPOREON underwent a spontaneous mutation and grew fins and gills that allow them to live underwater. They have the ability to freely control water.

FireRed / Shield: Its body's cellular structure is similar to the molecular composition of water. It can melt invisibly in water.

Diamond +2: It has evolved to be suitable for an aquatic life. It can invisibly melt away into water.

Platinum +2: Its cell composition is similar to water molecules. As a result, it can melt away into water.

HeartGold: When VAPOREON's fins begin to vibrate, it is a sign that rain will come within a few hours.

SoulSilver / X: It prefers beautiful shores. With cells similar to water molecules, it could melt in water.

Black 2 / White 2: Its cell composition is similar to water molecules. As a result, it can't be seen when it melts away into water.

Omega Ruby / Alpha Sapphire: Vaporeon underwent a spontaneous mutation and grew fins and gills that allow it to live underwater. This Pokémon has the ability to freely control water.

Sun: Its cells are composed of units much like water molecules. It lives close to water and is often mistaken for a mermaid.

Moon: Blending in with the water and erasing all signs of its presence, it patiently waits for its prey, fish Pokémon.

Ultra Sun: Clean, clear waters are its usual habitat. When it's about to be attacked by an invading enemy, it dives into the water to hide.

Ultra Moon: It detects nearby moisture with its fin. When its fin begins trembling rapidly, that means rain will fall in a few hours.

Let's Go Pikachu / Let's Go Eevee: Its cell structure is similar to water molecules. It melts into the water and becomes invisible.

Sword: When Vaporeon's fins begin to vibrate, it is a sign that rain will come within a few hours.

Legends: Arceus: Tests show that its cells closely resemble water molecules, which perhaps explains its ability to conceal its form while submerged. I believe the origins of mermaid folklore lie with this Pokémon.