These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Ear Worm: Practically all the songs as played on MAME, but the Boss theme is by far the most representative of this trope.
Funny Moments: After beating the boss of Florida, the cyborg scientist alligator, he becomes a bag. Also, the boss of the Chicago stage, a shotgun-toting mobster dog who wears a coat lined with knives, ends up getting smashed into one of the casks of wine in the background of the area you fight him in.
Goddamned Bats: The little blue guys with drill things on their heads and their pink electric variant. They have an rapid-hitting attack that is just slightly longer than your range, and tend to swarm you all over. Plus, the noise their rapid attack makes if it connects is very annoying.
The pink mobster dogs have an annoyingly dangerous bite move that they can use at any range, and it can hurt a lot. Thankfully, you can smack them out of it.
Game Breaker: The special combo attacks that the playable characters can use either via Street Fighter-esque button combinations, or by grabbing an enemy and hitting both the attack and jump buttons at the same time. They have massive priority (which means that enemy attacks won't stop them from being performed) and do tons of damage, enough to demolish bosses with only a few uses.
That One Boss: Ghost Buffalo, the boss of the Texas stage, due to its strange and unpredictable attack pattern.
Until you find out that there's a safe spot where the boss can't touch you with all but one of its attacks (the fireballs). This makes it a lot easier to hide from it when it's attacking.