Jigglypuff, a Balloon Pokémon. It has large friendly eyes and it sings a pleasant song.
– Ash’s Pokedex
I don’t know about “pleasant song”, but in the anime, the recurring Jigglypuff sings a song that puts everyone to sleep (because it’s using the move Sing), and then gets mad when everyone falls asleep instead of listening to its performance, and draws on their faces with a marker.
I found that Jigglypuff, and Jigglypuff in general, quite annoying. I don’t usually like “cute” Pokemon, I find them more annoying than cute. It’s the anime’s fault I think.