Touch anywhere on the left side of the screen for a floating stick: it moves your commando and aims in eight directions. On the right, the outer button is FIRE (hold it) and the inner one is JUMP. You can also flick the stick up quickly to jump; a slow push up only aims upwards. Hold down to lie flat, or to duck under water. Down + jump on a ledge or bridge drops you through it.

In Options you can make the buttons smaller or bigger and switch the flick-to-jump off.

Recruit: your commando takes 3 hits per life, enemies fire a little less, and you can retry a stage for free as often as you like. Veteran: one hit and you lose a life, like the arcade classics, with 3 free stage retries. Either way, the first stages are the easiest and the challenge builds up towards the alien hive. You earn an extra life at 20,000 and 50,000 points, then every 50,000.

Each stage has three checkpoints: two along the way and one just before the boss. "CHECKPOINT 1 OF 3" appears as you pass each one. Leave whenever you like (Pause → Quit to menu, or just close the game): the title screen then shows RESUME: STAGE n CP m and takes you back there with your score and gun. NEW MISSION starts over.

On the "Game Over" screen you can:

• Watch an ad to continue: 3 new lives at your last checkpoint, keeping your score and gun. At a boss, the boss stays as damaged as you left it.
• Retry the stage for free: from its start, with the score you started it with.
• Quit to the menu: your progress is saved at the start of that stage.

If no video is available right now (for example when you are offline), the free retry is always there.

After a stage clear you can watch an optional video once to start the next stage with a shield (14 seconds). If you only have the basic rifle, you also get the wide spread gun.

Shoot the flying pods and the sensor boxes to drop capsules: A auto rifle, W wide spread, B piercing beam, F flame spiral, R rapid fire and S shield (14 seconds). Your gun carries over to the next stage. You lose it with a life, except when you play as Kato.

Never during play, and there are no banners. A full-screen ad can appear after you tap NEXT on a stage-clear screen (never after stage 1), or when you quit to the menu after a game over. There is at most one every two and a half minutes, and none within a minute of a video you chose to watch. Videos only play when you tap a WATCH AD button, and the reward is given when the video ends.

Open Options and tap PRIVACY OPTIONS (ADS). It is shown where the law requires a consent choice. You can also reset your advertising ID, or opt out of ad personalisation, in Android Settings → Google → Ads.

Tap MEDALS on the title screen to see the 13 medals and how to earn them. Scores and medals stay on your device.

Your high scores, unlocked stages, medals, settings and saved checkpoint are stored on your device. They move to a new phone through Android's backup and restore (Settings → Google → Backup). They are lost if you uninstall the game or clear its storage without a backup.

All three can be switched on and off in Options.

Android 8.0 (Oreo) and newer, on phones and tablets. The game plays in landscape.