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.
The Mole Men, particularly those that jump around like mad, making them near impossible to hit. They're even worse in the export version of the game, as some of them take multiple hits to kill.
The Parcs clones in level five. You're given very little space to fight them in, making it much harder to avoid their grab attacks. And if they grab you, they'll throw you right out of the skyship, killing you instantly.
Freud Was Right: The thing that Clayborn keeps in his One-Winged Angel form's back to fire plasma bolts looks...familiar. Shouldn't be a surprise that this came from the same company that brought you R-Type.
Fransowors/Fatso, if only for her attack that not only drops a motorbike on you, but causes the place to shake like made, severely hampering your movement and making it much harder to dodge the bike.
Moguralian β/Gunpuncher. The guy has a melee attack that hits fast, has an extremely long reach and can kill you in around three hits. And when he's low on health, he'll start diving in and out of the ground, giving you a very narrow window to attack him in.