Here are some suggestions and thoughts.
1. Can you make him dance if 2 (or more) people dance around him (Like you did for Vilemaw from TT map)?
2. You can make Ascended Xerath yells 'Lightning bolt! Lightning bolt!' when he ults (?). It would be awesome!
3. I feel Xerath's damage is fine, but his health falls off in mid/late game (it is too easy to kill him).
4. Sometimes Ascension buff is granted to wrong person.