Alright, you've beaten up your nemesis. You want him dead, hopefully for a good enough reason to ignore my previous advice. There's just one problem. Remember how we said that the superhuman body reacts to near-lethal levels of damage by evolving defenses against it? That happens if you can't muster quite enough force to do the job instantly. Unless you totally curb-stomped the hero, you probably can't get through his skin or force field or whatever even if he's down. What to do?
Yes, that's right, the death trap!
I know what you're saying. "Mr. Big, that's so cliche. The hero always escapes those in the stories." Yeah, stop right there. Those stories are written by people who like the hero, so of course he escapes. I'm talking about the real world. Listen - if you lower a multi-ton pressure plate onto someone who isn't made of iron, he's going to die, plain and simple. I've lost count of the number of stupid villains who just decided to get a gun and shoot the hero, only to advance some Stage Two vigilante or Stage Three lowbie into the big leagues. Not only do they get thrashed and go to jail, but they leave this mess around for the rest of us to clean up. You guys know who you are. Cut that crap out.
There's one other thing working in your favor here. If the trap fails, you put a guy in a death trap instead of just atomizing him or something really lethal-sounding. The same cliche works for the public - they'll tend to discount the seriousness of what you were actually attempting. You'd rather look like a loony than a murderer to these people.
Here are the things you need to know about death traps.
First: The trap needs to be specifically designed to apply overwhelming levels of lethal force. I know you're all dying to try out your genetically engineered shark hybrids, or throw the hero into your smelting vat, or do some kind of wacky experiment. No, no, no. I cannot stress this enough. For example, who remembers the hero Magnum? He died, but his reporter girlfriend got tossed into a quantum furnace. You know what it did? It pushed her straight to Stage Four. The idiot villain who pulled this move is behind bars, and deservedly so. The trap needs to apply a huge amount of injury, quickly, before the body can recover.
Second: The trap needs to be geared for the hero's weakness, assuming he has one. If not, gear it for the hero's strongest defense. Again, I know what you're thinking. "Mr. Big, we want to kill the guy, not tickle him." Remember something really crucial here - his body is done adapting! If he was strong against fire before, that's about as tough as he's going to get if you do it right. And if he's specifically weak against fire, remember that he's weak because of his adaption. His body made itself this way.
Third: You shouldn't need to be around for the trap to work. In fact, you should get the hell out of town. Here's why: if it's going to kill him, it'll do so without your help. Unless your own abilities are powering the device, it'll work just fine on its own. Why leave then? He might escape it, sure. But if he does escape, where do you want to be? In the vicinity of an angry superhero who maybe even went up a Stage because you can't create an effective trap? Or in the next state over?
Some villains want to gloat at this point. Resist the urge. If you're totally sure that this trap will work, then ask yourself the important question: why is the hero still alive to begin with? If you weren't able to get him before, maybe you're wrong now. So just keep your mouth shut. You can always say a few touching words when you crash his funeral. Save the wit until then. If you really can't resist, at least take some time to polish it. Don't just improvise - work on it and rewrite it until it sings, then record it and have it played back automatically.
Some villains want confirmation that the trap succeeded. You need to have a level of confidence during the planning stage that it will, or you should avoid the attempt entirely. But if you absolutely want to be sure, station some video cameras and have them broadcast a signal. Wires can be traced, and you don't want to broadcast anything back which could lead people to your safe location. Not everyone has the electronics savvy to set something up like this, so again, don't do it unless you're confident of the results! That said, understanding surveillance electronics is a good general skill to have for a villain, so do try to take a class, or buy some books, or something that'll teach you how it all works.
For my money, the most interesting traps involve industrial machinery. This might take a little bit of travel depending on your home location, but scout out your city for abandoned buildings with machinery in them. Check out the power supply - sometimes they're still on the grid by accident. You can arrange a few backup elements of the trap, like a fuel-air explosive or bombs scattered around a factory, just in case the main elements aren't enough. Again, the key ingredient to a good deathtrap is a surge of overwhelming damage. If you're using bombs or other devices on a timer, make sure you have them scheduled properly.