It will take more than just a simple Shoryuken to get rid of these guys.
In God Hand any enemy, when defeated, has a chance of turning into a powerful demon. These demons have tons of health, do absurd damage, teleport around whenever you try to hit them, and just looooove to appear when you're low on health.
But then again, it's God Hand, you have to expect that kind of thing. It does help that when you encounter them at the end of the game you can kill them in one hit.
Super Smash Bros. Brawl has many Demonic Spiders in the single player adventure mode, The Subspace Emissary. Want to know the best part? They come in groups fairly often. Oh, and of course the higher difficulty levels make them faster.
And that's aside from the Cruel Brawl mode; a big group of intentional Demonic Spiders who not only deal twice as much damage as normal enemies, but are at least twice as resistant to your own attacks. Unlike Cruel Melee, where they had a weakness, the only guaranteed method of killing them in Cruel Brawl is to take advantage of some programming glitches and tricking them into killing themselves.
Floows recover damage when sitting still, attack from above, and any attack knocks them further upward. This means that every time you attack, you spend more time jumping and less time attacking, and if you knock them out of range they'll regenerate fully. Did I mention they're completely immune to energy attacks like Pikachu's Thunderbolt?
It doesn't help one bit that the damn things are kind of creepy.
The real pain is the Autolances. Their attacks are absurdly difficult to dodge and quite punishing.
No, no. It's the Gamygas. Those totem-pole beasties with five layers of bases and one giant face that you actually need to damage. The problem is that the face is so high up that a character can usually get in only one attack before falling back to the ground, and if a player decides to bring the face down to his level by attacking the bases, they quickly learn that Gamygas shoot ridiculously strong lasers at a rate of about two per second if they're not under constant fire. And because they're so tall, they take the prize for the hardest enemy to just avoid, even though they don't move from where they stand.
Ugh and you can't even attempt to trophytize them either because it seems like everytime you try, it shoots you before you can even throw it.
I don't think we can forget the Bytans, either. What with them always appearing in swarms, and then multiplying after a couple of seconds, so you literally get stuck in the middle of this never-ending swarm, whilst they batter your health up, ending up with you practically smashing your fist into the controller.
The Armanks. These tanks can only be harmed when they choose to expose there soft innards or to use their giant arms with long reach. Even if you manage to whittle down their health by attacking their powerful arms, the last hit MUST be on the fleshy innards, and between the occassional showing of this little green blob it's free to ram you and attack with it's arm while you're able to do no harm to it.
Squall's story mode in Dissidia: Final Fantasy is generally one of the easier ones in the game...except for these. Dubbed the Suicide Special Bartz by some fans, it's a Bartz manikin (Fallacious Wanderer, if you must), that via equippable accessories manipulates the game's damage meter and life bar to make it so that although one HP attack will kill them—their attack is obscenely high, so high that you cannot reasonably hope to chip it down to reasonable levels via bravery attacks, and high enough to guarantee a OHKO if they land one on YOU. Very few players do not hate them with violent passion.
Those types of Manikins exist in everyone's stories and the Terra ones are far far worse.
Also the level 90+ Warrior of Light Manikins you can find in the Shade Impulse chapters after clearing them with a 3 stars rank. They can dodge attacks at any time (except when they're attacking, but it will be hard to do), and when they attack you with a Bravery attack, they will always do a critical hit enough hard to break your bravery, getting so the bravery bonus (and they're always in the Omega version of the Order's Sanctuary, where the Bravery bonus are always equivalent to the breaker's bravery) and then finishing you with an undodgeable HP attack. Sometimes they throw you into an aerial battle instead of striking the last hit, but you can consider yourself lucky if you manage to hit them at least once before dying.
Jeff in the arcade version of Double Dragon and Chin in the NES version, are just as tough as recurring Mooks as they were bosses.
Robo-Ky in Guilty Gear X2. Normally, Robo-Ky is not a huge issue, but in Story Mode, he's a whole different story. If your character is unfortunate enough to fight him at the end of their story path, they'll discover that he is only vulnerable to Overdrives; special moves that take off a rough quarter of your opponent's health. Building up the Tension to use an Overdrive is an utter nightmare, mainly because Robo-Ky is aggressive as hell and will always unleash an annoying combo on you before you can land said Overdrive. Good luck hitting him with an Instant Kill too, because 9 out of 10 times, he will avoid it! Near perfectly by the way. The worst example is when Johnny has to fight him. Johnny, due to his lack of special moves and low combo-ability, will make it a living hell for the average player. Oh, and in Jam's story, she has to fight FOUR Robo-Kys!
Oh and Baiken's? You can't use instant kills either! Have Fun!