Vitreous

Vitreous is an old school shoot 'em up for PICO-8. Steer left and right and shoot at the approaching alien waves.

Collect seven power-up items to upgrade your weapon to the next level, up to 3. The upgrades also serves as shield — getting hit will knock your weapon down one level, and getting hit when at level 1 will cost a life.

At the end of each stage you get a choice for which one to warp to next. After beating a boss, the game loops back to stage 1, but you must defeat the three different end bosses to reach the final stage.