Harmful Park is known for being a rather cute and charming shmup, with loads of weird gimmicks and unique gameplay mechanics. It's also known for being one of the hardest titles to find for the PlayStation, though it can be found on the PlayStation Store thankfully.
Highlight Exit in the options menu. Then press, R1, R2, L1, L2, R1, L2, followed by Circle to access a Test Mode menu. Here, the player can go to any level, see any intermission and the ending, and view the bonus illustrations when completing a level perfectly.
The game's main executable, HARMFUL.EXE, has some small debug HUDs present at 0x1368 and 0x2780.
D OBJ= %d O OBJ=%d PRIM=%d DOBJ STS[%d] = %d OOBJ STS[%d] = %d PRIM STS[%d] = %d
SEQG=%d SEQ=%d SPRG=%d SPR=%d