Take a look at Dangerous Experiment:
In a game like the Vs. System TCG, your endurance total is extremely important. Even though players start with a whopping 50 points of endurance, 1 or 2 endurance can mean the difference between weathering a ton of breakthrough endurance loss on your opponent's big last initiative turn and shuffling up, dejected, for the next game. Players are constantly giving up the opportunity to strike back for stuns on non-initiative turns just so that they can prevent taking breakthrough endurance loss, and are willing to toss away three or even four cards with Break You so that they can sneak through a couple of extra points.
So why in the world would you want to play a card like Dangerous Experiment?
First of all, it's powerful. Any card that lets you name any plot twist you want and then allows you to put it straight into your grip can end the game instantly. Sure, given enough endurance loss, it can end the game in favor of your opponent. However, with the right calculations, it should not be difficult to make Dangerous Experiment work for you because you should regularly get exactly the card that you want.
Say that you need a Flying Kick to win the game on your initiative. Your opponent has set up his or her characters so that one attack in his corner will topple the entire board like a set of dominoes. You aren't representing any flying on the board, and all you need is that Flying Kick . . . How much would you be willing to pay in order to get it?
In this case, you should make an estimate as to how much endurance loss you are likely to cause given your planned sequence of attacks. Think about if your opponent is playing Boccio Burn or has some way on the board to cause endurance loss, like Pyro or Senator Kelly. Calculate how much endurance you are likely to lose from your own offense. Tally up the costs of all those characters with which you plan to swing. If you can knock the opponent to 0 endurance and still stay ahead, the endurance loss from Dangerous Experiment might as well be nonexistent. Winning a game is a binary system: either you win or the other guy wins. It doesn't matter if you win on 1 endurance because you hurt yourself with Dangerous Experiment, if you can set up the cards to put your opponent on 0 during the last turn. As much as you might like to win with a ton of endurance to show your complete dominance of your opponent, whether you have a lot of endurance or a little endurance at the end of the game does not really speak to the outcome.
What about if you need a Savage Beatdown to end the game? What if there is only one card left in your deck? In a case like this, Dangerous Experiment isn't so dangerous at all. What if there are two cards in your deck? Still not very dangerous. Three? Nope. You've tripled the number of cards you might see, and you will still be losing minimal endurance (assuming you have one or more Savage Beatdowns left in your deck, of course). The important thing to understand with a card like this is the how deeply in your deck you are likely to dig before you see the card that you want. Do you play the maximum allowable number of this plot twist? How many cards are left in your deck? How much endurance are you willing to sacrifice?
Another thing to think about is the relative cost of using Dangerous Experiment. Let's say your opponent is playing Sentinels and plays a Sentinel Mark IV on the fourth turn. That Sentinel Mark IV is likely to have at least 10 ATK. It might be pumped up with Combat Protocols. Your opponent might aggressively power it up because he or she has a Reconstruction Program face down in his or her resource row. The minute that Mark IV goes to 11 ATK, it becomes an eligible target for Overload. Now say that you have 48 cards in your deck and are playing the maximum number of Overloads. Your opponent is sending that Mark IV at your poor Vulture and you are going to take a ton of breakthrough endurance loss. It probably makes sense to go for the Overload. Instead of taking 10 or more endurance loss and losing your Vulture, you can find Overload and stun your opponent's best character. It's unlikely that you will take a lot more than you would if you just accepted the hit, and this way, instead of Mark IV beating on your Vulture and being ready the next turn, you have a Vulture to send into your opponent’s precarious X ATK/1 DEF lineup (where you are eligible for some precious endurance-pumping breakthrough), and he or she will be without his or her best character. If you send Vulture after Longshot, what choice is Mr. Sentinel going to make?
There are a lot of applications. I think that the best ones will be where you can "cheat" into board advantage. A lot of what makes the Vs. System TCG tick is stunning two of your opponent's guys and having only one of yours go down, or "stealing" a stun by stunning one of his or her characters when he or she isn't expecting it. If Dangerous Experiment might let you pull a fast one, do the math. Are you likely to be better or worse off if you get what you want? What will it cost you to set up this play? What is the relative cost? Will the character that you stun be likely to cause more or less endurance loss than Dangerous Experiment, and on what timetable? How much of an advantage is that going to mean next turn? Much of the time, playing this card will be a simple choice. You might be able to win immediately and have a low chance of doing any serious damage to yourself. In that case, you go for the win. You gamble, you take a little endurance loss, and you punish your opponent.
The last major application of Dangerous Experiment is when you have a particular card that your deck needs in order to function properly. In this case, Dangerous Experiment can serve as your fifth, sixth, seventh, or eighth copies of a deck-enabling plot twist. How much endurance would a Sentinel deck be willing to pay to always have Longshot on turn 1? Not every deck that depends on a certain plot twist can wait for Alfred Pennyworth to ready in order to win under pressure. In a deck where you can win immediately with mechanics that do not interact directly with your opponent's board, Dangerous Experiment is indeed deadly for your opponent, no matter the cost.
But never forget that this is a Dangerous Experiment. Look at the picture. Doc Connors was a bright guy. He figured he could splice a little reptile DNA onto himself and grow back his arm. He was right . . . but better off if he didn't try at all.
The one thing you will have to be wary of when playing this plot twist is, What happens if I get what I want? Always ask yourself, What does this cost me? Sometimes, mind you, not very often, you have four copies of the plot twist you need . . . and they're the bottom four cards of your deck. Sure, you'll get the Flying Kick, Savage Beatdown, or Mega-Blast you wanted, but it might have been better if you didn't try. Never forget that even when you do the math, the reason that games like the Vs. System are interesting is because of the presence of some amount of random chance. Just as you can find glory in the victory of a desperate topdeck, even a correctly played Dangerous Experiment will wreck you some of the time. That element of risk is why they didn't call it Controlled Experiment.