Drifloon, the Balloon Pokémon. Drifloon is filled with air and can either expand or shrink to express its feelings. It also likes damp weather.
– Dawn’s Pokedex
I like Drifloon’s design, mostly, the X for the mouth. Despite it looking cute, its Pokedex entries are rather ominous, talking about it being formed from spirits of people and Pokemon, and stealing children away (ie take them to the underworld) who mistake it for balloons. Drifloon and its evolution have the unique type of Ghost/Flying; while it has 5 weaknesses, it also has 3 immunities, the most a Pokemon can have based on typing alone.
Stat-wise, it has good HP, Speed, and Sp Attack. One of its abilities, Unburden, can make Drifloon very fast, especially if it holds the Salac berry. Despite being part Flying though, Drifloon doesn’t learn many Flying moves; it can’t learn Fly, I guess because it floats like a balloon rather than fly like a bird.