This morning the North American version of the Marvel Tsum Tsum Mobile Game was updated to add Loki and also announce that Doc Ock will be coming soon!
One interesting thing about Loki is that, instead of having an "easy" level, he has a "chaos" level that is even more difficult than expert.
The official Marvel Tsum Tsum Game page posted a Loki preview video
In addition to announcing Loki, the official page also announced
that the game servers would be down for maintenance from around 12am - 3am (Pacific time) early tomorrow morning (9/29/2016). This maintenance is related to a new version of the game (2.1) which will add some future Tsums as well as an upcoming event! So sounds like we will be getting our first event soon!