po-devs/po-server-goodies — pull request #609 by ROMaster2 (2014-01-12 21:56:42+00:00)
Title: Adding Pokemon to Sky Battle

As according to http://www.serebii.net/xy/skybattles.shtml

Ho-Oh, Lugia, and Rayquaza are excluded from the whitelist as they're Ubers.

On a side note, Thundurus-T can float but probably hasn't been tested by Serebii yet. I didn't add it to the whitelist but I do anticipate it to be at some point.