As stated by Chrales, he tricked the game client to believe that his Pokedex is filled and shows Ho-Oh and Celebi as already caught. When he did this trick, he could render 3 new 3D assets of Ho-Oh and Celebi, 2 normal skins and one shiny. Ho-Oh is with normal and shiny skin, like Mewtwo, while Celebi shiny form is not available, like Mew.
The gender circles are a bug, as Legendaries should not have gender.
Unfortunately, their 2D icons are not added yet, so as soon as these icons are added, Ho-Oh and Celebi will join Pokemon Go.
For last, we expect to see their CP and Max catch CP as follows:
- Ho-Oh – 48276 CP and Max catch CP 2222
- Celebi – 37733 CP and Max catch CP 1766