Wailmer is a spherical whale Pokémon with no tail. It has a dark blue topside and a tan underbelly with grooves. It has two fins that have finger-like appendages, baleen plates that resemble teeth, and a pair of nostrils on the top of its head functioning as blowholes.
Wailmer stores water inside its body, which it expels through its nostrils to startle people. When storing water in its body, it can turn into a bouncing ball. The more water filling its body, the higher it can bounce. It becomes lethargic when it is dry. It swims with its mouth open and eats tons of food a day, such as Wishiwashi. It lives in the sea, and can only live on land for a short amount of time. It occasionally bounces onto the beaches to play. On rare occasions, pods can be seen washed up on shore — a result of genetic memories of having once lived on land. Dhelmise and Sharpedo are natural predators to Wailmer, and Cetoddle is thought to be its close relative.
In The Great Eight Fate!, a Wailmer was part of Juan's Sootopolis City Water Exhibit. It and Juan's other Pokémon were captured by Team Rocket, but they all worked together to escape.
In Island Time, a Wailmer befriended Robin and eventually evolved into a Wailord in order to transport him, Ash, and his friends to a ship heading to Ever Grande City. However, Robin later decided that he wanted to go back to the island he was living on.
In Pruning a Passel of Pals!, a Coordinator's Wailmer competed in the Battle Stage of the Wallace Cup. It went up against Dawn's Buneary and lost, allowing Dawn to advance forward in the Contest.
In Leading a Stray!, a Wailmer was trapped in the sewers, but it was rescued by Ash, who later helped it rejoin its family in the ocean. It evolved into a Wailord in the same episode.
In Yo, Ho, Ho! Go, Popplio!, Professor Kukui, Kiawe, and Sophocles used two Poké Ride Wailmer to travel around Melemele Island.
In The Island Whisperer!, a Wailmer was attacked by a Bruxish's Psychic powers and was subsequently stuck in-between a rock formation in the sea.
Six Wailmer appeared in JN143, one of them evolved into Wailord after being freed after getting trapped.
Wailmer debuted in Pikachu's PikaBoo.
In Pokémon Heroes: Latios & Latias, Ross used a Wailmer during the Tour de Alto Mare. It and Ross came in second, while Misty and her Corsola came in first by a mere centimeter.
Two Wailmer appeared in a fantasy in Johto Photo Finish, during Harrison's explanation of the Hoenn region.
Wailmer physically debuted in the main series in Hoenn Alone!, where multiple of them were swimming in the ocean.
A Wailmer appeared in the opening sequence of Destiny Deoxys.
In Clamperl of Wisdom, multiple Wailmer were living at Maisie Island.
Three Wailmer appeared in The Relicanth Really Can.
Multiple Wailmer appeared in The Evolutionary War.
In Pokémon Ranger and the Temple of the Sea, multiple Wailmer were present during the final showdown with The Phantom and his crew.
Multiple Wailmer appeared in Giratina and the Sky Warrior.
In One Team, Two Team, Red Team, Blue Team!, a student used a Wailmer provided by the Pokémon Summer Academy for the second leg of the Pokémon Triathlon.
Multiple Wailmer appeared in Kalos, Where Dreams and Adventures Begin!.
Multiple Wailmer appeared in Diancie and the Cocoon of Destruction.
A Wailmer appeared in Alola to New Adventure!.
Three Wailmer appeared in a fantasy in Yo, Ho, Ho! Go, Popplio!.
In Filling the Light with Darkness!, a fantasy of a story from the past featured a Wailmer. It reappeared in a similar fashion during The Prism Between Light and Darkness!.
In Securing the Future!, a Wailmer joined the rest of Alola in showering Necrozma with light so it could return to its normal form.
A Wailmer appeared in Pikachu's Exciting Adventure!.
In Narrowing the Chaser Chase!, a Wailmer was used to transport Ash and Goh to Sea Mauville so that the latter could participate in a Project Mew Trial Mission there.
||Wailmer, the Ball Whale Pokémon. Wailmer loves to startle people by storing water inside its body, then expelling it through its nostrils.
||Wailmer, the Ball Whale Pokémon. It spouts water out of its nose and becomes lethargic when its body becomes dry.
Pokémon: Twilight Wings
In Early-Evening Waves, two Wailmer were living in a lake where Nessa was doing a photoshoot.