TeeWorlds

Free online multiplayer game. Battle with up to 16 players in a variety of game modes, including Team Deathmatch and Capture The Flag.

You can change touchscreen controls in Settings → General, there are six control layouts available.
You can change button positions at startup in Change device config → On-screen keyboard → Change layout.

To play on some servers, you need to press Back → Join red/blue, after connecting to server.

Supports gamepads, supports mouse+keyboard controls.

Sources: https://github.com/pelya/commandergenius/tree/sdl_android/project/jni/application/teeworlds