Zanac/YMMV

Zanac has some things that are subjective:

Demonic Spiders:
- Round Cores in the original, when they're fully open. They release projectiles which spin around, soak up quite a few damage and can overwhelm the player.
- Also, for normal aerial enemies, purple Lusters which fly around with a wise arc and that means usually firing its projectiles behind the player.
- Jack the Dynamic Difficulty high enough and you get these annoying blue enemies that line up with you and shoot out a constant stream of missiles. Flying above them will NOT help because they can fire upwards too.
Game Breaker: Weapon 7. Fired fast, could move left and right at a limited angle, and could go through enemies. Very powerful, but is also a bit of a rarity.
Goddamned Bats: Although many of the enemies qualify, T-Cells, which appear in Areas 8 and 11 in the original game, are perhaps the best examples. They cannot be killed with anything that doesn't clear the screen, they block shots completely and have to be destroyed by bumping into them.
Goddamned Boss: Capital ships in the original game since almost all projectiles bounce off of it (although still damaging it), lowering your fire rate considerably. In addition, all but one of those will actually home on ship.
Most Wonderful Sound: The extra life sound. The Neo variant even has a ringtone for it in Japan.
Scrappy Weapon: Weapon 2 in Zanac, a shield that lasts for 50 uses, can be recharged by collecting more '2' items, but also triggers the Dynamic Difficulty's Berserk Button.
Sequel Displacement: In fact, the first port was the MSX one.