Darwin is an unkillable Mutant.

Darwin is unkillable because he can adapt to anything. His mutant ability is known as Reactive Evolution, which allows him to adapt to any environment as long as it allows him to live. 

Simply put, he cannot die because his body will adapt to his circumstance and stop his death. If he is going to die of old age, his body simply won't age. If you shoot him, his body becomes able to deflect bullets. He cannot drown because he will grow gills. He cannot die from anything. Con will have to state a way he could die, and I will easily disprove it.

My first point, is my weakest point. It’s the fact that “plot armor” rises above OP-ness.

Darwin is an “unkillable” mutant. Except, not really. Darwin is a character… in a comic book. And, in comic books, nothing is invincible, invulnerable, or immortal. The Flash outran death, the Green Lantern made his own ring from an abstract concept, and Darwin has already died. In X-men: First Class, he had one of the most disappointing deaths I’ve ever seen in Marvel. And, if he can die in a movie, written by people I can only assume  have never read comic books, he can die in any medium. If Disney can destroy the image of Luke Skywalker, Marvel can, and has previously done, the same for Darwin. The writers, for good or ill, are the gods of these books. Darwin is only “unkillable” when it’s convenient, but as soon as it’s not, he can die too.

 Beyond the scope of plot armor, Darwin can likewise be killed by time travel. Though his mutant power can allow him to adapt and evolve according to any obstacle to his survival, his mutant gene didn’t become active until his preteens/teens. Hence, while he might theoretically be able to handle Hulk, Thor, Galactus, Thanos, and any number of enemies of the highest level of strength, the requirement for this “op-ness” only activates years into his life. That translates as years to kill him.

Plus, if he truly posed a significant threat, and since the timeline of Marvel is so… fluid, I can think of like eight people capable of using this method to kill Darwin, namely Kang. If there’s some unbeatable hero that could stop his conquest and rule, he wouldn’t be the menace he truly is.

Even if you time travel back in time to kill Darwin before he activates his mutant gene, the already existing Darwin will evolve to fit into the timeline. Plus, you would probably break all reality, and still not kill the man. Now you must understand, the disappointing death he had in that X-Men movie does not mean he is killable, as it never states he is dead. What if he just became energy in order to escape death? And if he was dead, this still does not make him canonically killable. As I said previously, he will literally just adapt to anything, if I went back in time to kill him before he had his ability, him now would adapt to fit the timeline. I believe the movie Darwin just adapted to escape that shitty scene and became raw energy. 

Let me give an example of an overpowered character that could not kill Darwin:

Hel, the literal goddess of death. With one touch she could kill you. This is what she did to Darwin, she touched him. And he became a God of death just so he could escape death. That is how powerful his ability is.

Interesting counterpoint. Nevertheless, I'll shift the debate to other, more entertaining matters.

Firstly, I think we should clarify a couple of things. Darwin's power is, as defined by pro, Reactive Evolution. This has certain connotations that we didn't get into though. Namely, that evolution doesn't necessarily guarantee an improvement in an entity, but merely change it so as to ensure survival. In the case of Darwin, this could manifest in a multitude of ways. Pro mentioned that if shot with bullets, Darwin could become bulletproof. Not completely true. The threat of the bullets, being recognized by the mutant gene as life-threatening, could instead make it so that Darwin shares jellyfish-like properties, where the bullets aren't able to be as lethal as they would otherwise be to an organism with internal organs. In the case of Darwin vs Hel, Darwin didn't become powerful to defeat Hel, instead he grew to a level where the present threat wouldn't be capable of ending his survival. A similar storyline could be argued for where Darwin's mutation simply caused Hel to forget/ignore his existence. Pro, if I'm not mistaken, seems to entangle survival capability with power. That's incorrect. Power isn't the defining trait of survival for creatures. As Charles Darwin himself put it, "it is not the strongest of the species that survives, nor the most intelligent; it is the one most adaptable to change."  Additionally, Darwin evolving doesn't necessarily ensure permanent change. He is, again, an adapting force. Take Pro's example about guns again. If bullets were shot at him, his powers might kick in to make his skin become so incredibly dense to resist the bullet's penetrative powers, this would also lead to a weight change. Now, imagine that directly after, Darwin is in an aquatic environment. Sure, his powers might manifest to give him gills, or it could make it so that he is so light that he can walk on water. Again, the defining factor of his power is that it is Reactive, which forces me to assume that he has little control over it. Yet, even if he did, I would argue that such a quality would be even more vulnerable to my attacks on this debate. With this clarification in mind, I think the audience understands that the survival outcome, not power disparity, is what changes by the manipulation/activation of Darwin's power.

Now, with this in mind, I'd also like to put focus on the term "reactive". To the Pro, I ask, what is reacting, and what is it reacting to? It's not Darwin himself, for the change seems to take place without his control. So then, is it the mutant gene itself that is reacting, like some type of 6th sense similar to the Spidey-sense. As for what it is reacting to, I must assume that it is something life-threatening, as Pro assures me the Reactive Evolution power is something that guarantees endless survival. In that case, to what extent does this "sense" detect. Pro, in their rebuttal in Round 3, seems to indicate the "sense" can detect threats at the space-time level. Fascinating theory, not sure if I can agree though. That said, even in the hypothetical situation where the "sense" is able to detect dangers to the present Darwin as seen by the experience of past Darwin, that adaption to timeline changes relies on, and represents, a direct threat to Darwin's life. In that case, how would Darwin's power react to the application of an inhibitor collar, the likes of which we've seen in Deadpool 2, and which doesn't pose a life-threatening danger directly, but indirectly? Would the collar not enable to deactivation of the mutant gene, along with the "sense", and allow Darwin to be killed?

He just doesn't die. It really is simple. Even if his body does not react the way I said it would, and even if he has no control over it, it still prevents him from dying. Now the point of a power deactivator is very interesting, and it causes me to think if his power is capable of "foresight" or seeing a threat before it happens. I think that his power would adapt to be not de activated, as it would sense that someone is trying to harm Darwin. So would this make his power symbiotical? I am starting to confuse myself. 

I beg to differ. In your final argument, you thought about the theory of foresight, and I think you acknowledged it as more than a possibility, but not quite a fact. That's fine. I can prove it's not capable of foresight, and therefore not capable of preventing Darwin from getting his powers de-activated, and consequently killed.

If Darwin's mutant gene was capable of foresight, of knowing what life-threatening events would happen in the future, he would have been as powerful as every villain he would ever face, the very moment his powers manifested. It wouldn't depend on being face-to-face, present in time, directly in confrontations with them, like he was with Hel, or would be in the hypothetical timeline situation. That opens the door that though Darwin's power has instant reactions, it's only in the presence of something imminently life-threatening. As far as his power adapting to not being de-activated, we've previously confirmed that it operates solely on a life-or-death basis, and simple having de-activated his powers doesn't mean the person who put them on intended to harm him, or even that he would be harmed. I mean, in the context of this debate, certainly, I'm aiming to kill him after all. But he could be going undercover in mutant prisons, trying to pass as a normal human, or even doing some experiments with Beast that unfortunately ends with him dying as an unintended happenstance. If your sole argument is that his power would sense the danger or intent before being de-activated, I've just poked a hole in it, and that means it's possible, at least according to our current understanding of his powers.

To conclude, his powers are cool, I agree, but he's certainly not unkillable. I had fun in this debate, though, and I'd be interested if you have any more comic topics you'd want to discuss. Good luck in the vote!