Heimdall serves as an announcer for the Ragnarok tournament, technically he is also a god. He's easily the shortest character in the manga and with his unusual appearance there's potential for quite a variety of voicing options. For Heimdall it'd be interesting to hear your own interpretations, but you're seriously stuck for ideas my suggestion would be a kind of pitched Roz from Monsters Inc. If you come up with an idea on how to voice him then feel free to resubmit, if you've already submitted an audition.