You can play Shootup.io in a99.io as unblocked.
In Shootup.io game, you have to be 1st in the leaderboard and keep this 1st. You will not notice how your time passes while playing games. You can kill the zombies that you encounter with your pistol, Sniper, Scanning rifle, Heavy Machine scanning and Rocket. The more zombies you kill, the higher you will be ranked according to the leaderboard. You can move with "W, A, S, D" keys.