- Admit it, you jumped a little upon first seeing the character select screen◊ for Metal Slug 2/X & 3.
- In fact, a lot of the artwork is pretty disturbing. Think Monty Python animations, only in a war time setting and (mostly) not played for laughs.
- Metal Slug 2 (or X) is where the supernatural elements start coming into play. They're not too bad until you reach the train passage route and end up having to make your was through a mutant infested area who will explode in a attempt to take you out.
- Mission 2 of both Metal Slug 2/X and Metal Slug 3 in general. Not only are the levels filled with undead beings (mummies in 2/X, zombies in 3), said undead beings can turn your character into one of them (granted, your character still remains controllable as a mummy/zombie). Mission 2 of Metal Slug 3 adds more nightmare fuel with the level music, which sounds noticeably dark and creepy fitting for a zombie-infested plane crash site, caused by an alien meteorite.
- In a combination of this, Squick, and Nausea Fuel, several of the zombies attack with infectious vomit but only two variants (female zombies and one of the civilian male zombie types) of them puke it out. The others expel it via violently tearing open their ribcage (fat zombies), squeezing their head until it pops out of their brain (the other civilian male zombie type), and most gruesomely pulling out their guts like a hose and squeezing it out (doctor/scientist zombies).
- The Bloody Murder special attack zombified players get: The zombified hero vomits up a horrifying amount of blood.
- The zombie soldiers are especially terrifying with a much more menacing look about them, and unlike the slow moving ones, will actually bum rush you in a suicide attack that can turn you into a zombie if it hits. Thankfully, they're only found near the end of 3's second level, but still...
- They also appear in the final stage. To be more specific, they're zombie clones of your captured comrade: I.E, zombie clones of your friend. And by virtue of being clones of a playable character, they get the blood vomit special attack, too. Making things worse is that said segment is you on the run to escape the now self-destructing mothership and having to destroy barricades as the zombies keep coming. On single-player, this is both horrifying and utterly difficult.
- If you thought it wasn't bad enough, Metal Slug 4 features both mummies and zombies in Mission 4 (granted, you only encounter one type depending on the path you took).
- A lot of the deaths are animated in disturbing detail; lighting people on fire in particular.
- Special mention goes to the animation for when you get hit by a zombie's attack if you're already zombiefied in Metal Slug 3's second level. It has the player character's head fall off. And if you're in the air while it happens, your character explodes like the rest of the zombies' death animations.
- Are you claustrophobic? Do you hate bugs? Then be very careful which route you choose on Mission 4 in Metal Slug 3.
- Every time a stage is accompanied by "Metamorphosis", you know some disturbing things are about to come down.
- Metal Slug 3D's final stage. Dear God. It is a Womb Level with wet flesh everywhere. The cutscene after you beat the robot boss in the first part also counts.
- The Evil Spirit Incarnate, the Final Boss of Metal Slug 5. This... thing comes from nowhere, has a hellish screech, and it leaves just as quickly as it appears. It even looks nightmarish, with its red eyes, Celestial Body, and it has a giant human skull on its chest, not to mention the giant scythe it holds. And what even is this thing? Is it the Grim Reaper? Is it some sort of demon god? Or something else entirely? The fact that there is absolutely no info on this thing doesn't help at all. Perhaps the only comforting thing is that it is driven off by normal human weaponry note .
- On the subject of final bosses, there's Rootmars, the leader of the Mars People and the final boss of the third game. For starters, he's not exactly the prettiest alien you'll ever meet, with special mention going to the fact that his brain is visible and sticking out of his head. His entrance is rather unsettling as well, given how he flies in from nowhere and cackles madly before doing battle with you. That said, the fight afterward will likely give you dreams of a much better kind.
- 6's version of "Final Attack", which is essentially a Dark Reprise of the aforementioned theme. It starts out like every other version of the theme, only for it to change into something more creepy.
Nightmare Fuel / Metal Slug