Captain Kalliope Flies Again by Aristaeus890 is a classic SHMUP for PICO-8.
The story of the game follows Captain Kalliope, who has once again been captured by his arch nemesis, and once again has knocked out a dozen guards to escape on the experimental QT31 Biplane. If you run out of ammunition, the QT31 will helpfully switch to another completely random weapon at its disposal. You can pick up the crates to either restore your ammunition, or switch to a random weapon. If you take damage, you’ll enter into crisis mode. After a few seconds, the QT31 will extinguish any fires and repair itself to nearly new, do this too many times, however, or get hit again while repairing it, and it’s down in flames. You can try Hypermode for a first try.