Closed beta, first wave
The server is up and the Android build is on the download page behind a Groot ID. No end date: this wave runs until the next build is ready.
This wave is narrow in what it tests rather than in who can join it. Its job is to find the failures that only appear when a real device on a real network talks to a server that has never had one, and for that it wants variety of hardware more than it wants a queue.
How to join: sign in with a Groot ID and take the build from the download page. There is no invitation to wait for and pre-registering is not a requirement.
What to expect has grown since this wave opened. Sign-in works, an account is created and kept, the game is handed all of its data, and quests, summoning, deck editing and unit growth are built. Each device gets its own account rather than sharing one. Treat what is in it as scratch all the same: the world is cleared before it opens properly.
What to send back: what you did, what happened, and what you expected instead. Device model and Android version help most, because the failures worth catching at this stage are usually specific to one of them.
The wave has no closing date. It ends when the next build is ready to take its place, and that is announced here.