There is a popular myth that supervillains are invulnerable. This is completely false. Invulnerability is a superpower in it’s own right, and it is one of the less common ones. This myth is propagated by comic books depicting costumed superheroes being defeated over and over again by evil, invulnerable villains.
Aside from the ridiculous costumes these heroes tend to make the mistake of taking on these villains, alone, in hand to hand combat. They are then soundly beaten as a result of overwhelming odds. Even if the villain is the armed one, the hero thinks he can take them down with nothing but his superpower.
This never works. Whoever has a gun is going to be shooting, and whoever does the shooting typically wins. This is why supervillains seem so invulnerable, because no one has actually bothered to try and kill them.
So. Rule one of killing supervillains. Get a gun, and shoot them. A bullet through the heart should do nicely. Some villains may need to be shot more than once. Some villains are very fast. Extraordinarily fast, in fact. An automatic machine gun is the preferred weapon in these cases.
Some villains may be armored. The trick in these cases is to find the weak spot. There’s always a week spot. The belly, the neck, something. Don’t say it’s impossible, find the weak spot and exploit it. This applies to both natural armor and artificial. Armor does not constitute invulnerability, just defenses, and defenses can always be breached.
Some villains are actually invulnerable. There are two cases of these. One is the actually invulnerable type, the super healing, or the one that can eat bullets and spit them back out without suffering ill effects, or the extremely rare and particularly nasty undead. It’s hard to kill something that’s already dead.
I’m not going to talk about the undead because I’ve yet to see one that posed an actual threat. In fact, I’m not sure I’ve seen one at all. Invulnerability, however, is a serious problem. Super strength is a similar and equally dangerous property. When dealing with a villain possessing super strength or vulnerability get out of the area as quickly as possible, and experiment with dropping various types of bombs on top of them. Alternately, strap them to a rocket and try ejecting them into space where the quarantine police can deal with them.
The other type of invulnerability applies to villains with metamorphic abilities. They’re made of sand, or glass, gravel, or something that hasn’t been thought of yet. If you shoot them they simply collapse into whatever basic material their physical form is made up of. Hand-to-hand combat is especially useless in these cases. If this metamorphic property is compounded by some kind of super strength then you have a deadly force to be reckoned with. Fortunately, these types are very rare. Metamorphs tend to tire easily.
Tiring a villain is one thing, but taking advantage of that is something else entirely. What do you do with a heap of shattered glass that simply behaves the way you expect glass to behave? This information can be applied to elemental as well, and it involves understanding the basic laws governing the world around you. What is the weakness of the form that the villain is currently existing in? How do you destroy glass or sand? Tire your villain out, and then throw he or she into whatever situation would usually destroy the substance they’re inhabiting just as if it were inanimate.
Rule 1 of Supervillain killing is to try shooting the thing.
Rule 2 of Supervillain killing is that everything has a weakness. Find that weakness and exploit it.