Seriously Mew, you and Braixen are getting late if you can't decide which costume you will wearing.

In the first Pokémon movie, Mewtwo Strikes Back, Mew is voiced by Koichi Yamadera, who voices some characters (human and Pokémon alikes) in every Pokémon movies. (However, he was always replaces by English voice actor in English dub for the human characters he voiced)

This 4koma involves Mew dressing up as other Yamadera's characters, as shown in order:
-Spike Spiegel (Cowboy Bebop)
-Beerus (Dragon Ball series)
-Ryoga Hibiki (Ranma 1/2)

Here's also the minor one for Megumi Hayashibara in the 4th panel; Serena's Braixen is voiced by Hayashibara in the Japanese version of the main anime's XY seasons. Here, she's dressed as Anna Kyoyama from Shaman King.

Pokémon is belongs to Nintendo, GAME FREAK and the Pokemon Company.
Cowboy Bebop is belongs to Sunrise.
Dragon Ball series is belongs to Akira Toriyama, Bird Studio, Shueisha and Toei.
Ranma 1/2 is belongs to Rumiko Takahashi and Shogakukan.
Shaman King is belongs to Hiroyuki Takei and Shueisha.