The only events so far are:
- Hidden Ability Mega Torchic (concluded)
- PokeBank Celebi (basically unreleased)
Also the Pokemon that appeared in the Hidden Data (Vivilions with different patterns, AZ's Floette, Mega Latios/Latias etc.) that Smealum found are rumoured.
Everything else you've heard is basically fake as of yet.
Hope I helped. :)