Prototype Three: Invincibility

You're a guardsman who has to defend an outpost from otherworldly beings, if you get surrounded you lose, if you don't, and you manage to break the games AI, you win

you cannot get damaged, therefore you can get into the faces of the entities all you'd like and you'd be perfectly fine. On another note most of the entities are killable, though their hitboxes may be a bit hard to hit, just keep aiming for the center and you'll likely be able to kill them. (do keep in mind the entities do respawn)

wsad to move, esc brings up the pause menu (which you can use to quit the game), left click to shoot.

If the AI breaks, just quit to menu via the pause menu (escape button)

Sidenote: the big entity that wanders into the middle of the corridor emits an energy shield that is basically invincible, if you have trouble shooting past him just walk past (or over) the big green creature with the shield