The only sound that most Pokemon creatures make is that of repeating their names.
If I were to ever create a Pokemon character, I would make one with a head ornamentation that looks a bit like an ax. I would then name it, "It hurts", or rather, "Itherts." He's not really in pain, of course. It would just be funny when he says his name.
Btw, I've based this creature on an baby aye aye. I've always thought all baby mammals were cute. I was wrong. Google baby aye aye images if you want to be horrified.