Unglings are usually minor characters but they have several episodes planned to focus on them. They  are a group of creatures that don't have much of a brain, and just copy everything else. They keep copying behaviors until something slaps em and then they'll never do it again.  The voice should be something that sounds not very human at all. They just make sounds that resemble language but it's just nonsense.  If you need inspiration I recommend checking out https://www.youtube.com/watch?v=eGPI76PVjnw&feature=youtu.be