Invasion is the first minigame of MicroVolts and the first PvE (Player VS Enemy) mode. It only allows one player.
In Single Wave, the player must clear waves of enemys. On every fifth stage (up to 10 on easy, up to 20 on hard), a boss appears.
Single Wave(Hard) can only be played three times a day. If you use up your three tries, you can't play it again for 8 hours. If you lose, the game is over. You can play Single Wave(Easy) as many times as you want.