9spaceking would definitely beat seldiora in a debate.

Statistics: If you look at 9spaceking's winrate, it is 60%, a reasonable amount, However, seldiora has lost more than 80% of his debates. Even against a random debater, seldiora would only have 20% of winning. But combined with 9spaceking's experience with over 300 debates under his belt, seldiora has no chance of winning. It's just simple statistics, is all.

Topics: If you look at the topics taken by seldiora, he concedes a vast majority of debates, thus reasoning that he would take the opposing side to 9spaceking's usual forte. However, he would lose motivation as the opposing side is not what he usually is used to. Because he would have to research the new side ahead of time, 9spaceking could easily anticipate this information and the research would have to be nearly flawless, otherwise 9sk could poke holes in seldiora's arguments. Due to cognitive bias, seldiora would have a tough time battling 9spaceking who would be arguing his usual side of his stance. 

self-contradictory: Seldiora seems to be pressured under more serious debates. But even in his best debate on DART (https://www.debateart.com/debates/2264-tournament-r1-seldiora-vs-supadudz), he presented three points to help con, which even Whiteflame discouraged. Look in contrary to 9sk's best piece of writing, about how smoking should be banned. (https://www.deviantart.com/sel-diora/art/Puff-of-Death-458177289 -- I know it's my username but I changed it from long ago) Though a controversial topic, he notably pointed out the errors in people's thinking in "their body their choice", and invoked both feeling of distraught when smoking, along with environmental concerns. On the other hand, seldiora has failed to negate a similar resolution of "your body your choice" contention in Abortion, losing severely against Ragnar. Seldiora's research on the opposing side is extremely poor in comparison to 9sk. Take a look at this debate about banning assault weapons: https://www.debateart.com/debates/2231-resolved-citizens-shouldn-t-be-allowed-to-have-assault-weapons, seldiora only listed a few bare bone facts and only tied against his opponent. Looking at 9sk's research in comparison, he thoroughly analyzed countless areas and experts, listing a lot of convincing examples why gun control policies are bad, [https://www.deviantart.com/sel-diora/art/The-Ineffectiveness-of-Gun-Control-Policies-592871880] which would completely and utterly defeat seldiora's argument in this debate. 

Perhaps the best example of exactly how this would play out is https://gaymarriagedebate.jimdofree.com/, where pro is 9sk and con is a seldiora way of debating. Despite trying to push the Burden of Proof onto pro, con still established a case which slowly was tore down with illogical reasoning and numerous fallacies. In the end, pro upheld the idea that gay marriage should be implemented. Indeed, if you look at this similar debate which also concerned Incestuous marriage, (https://www.debateart.com/debates/2227-support-same-sex-marriage-endorse-incestuous-marriage-just-the-same) despite facing someone with similar amount of debates and winrate, seldiora still lost immensely, showing his lack of ability to argue the opposite in what he believes in.

Conclusion: Seldiora is self-contradictory and helps his opponent countless times through debates. He has far fewer debates than 9sk under his belt on DART, and has failed to win against even lower ranked debaters. Just how can he possibly win against 9sk?? He has no chance. 9sk will win beyond the shadow of a doubt.

Let me make my argument simple, the resolution is impossible to prove no matter how good 9spaceking is. Let me just describe the examples with what could happen:

Seldiora Wins:

-Seldiora provides an argument and then shoots his past self, causing both of them to forfeit

-Seldiora traps his past self in a prison cell and then makes an argument, causing only 9spaceking to forfeit.

-9spaceking forfeits

-Seldiora makes a better argument than 9spaceking

Both of them tie:

-9spaceking is hit by a bus and Seldiora is shot in the head by BearMan

-Both of them full forfeit

-Both of them make equally good arguments

-Everyone on DART besides 9spaceking and seldiora are targeted by the Mafia and killed, therefore no one can vote.

-Nobody votes regardless.

Bearman's advice causes massive time paradoxes and are impossible to resolve. If seldiora shoots 9sk dead, wouldn't he be unable to make the argument in the first place? If seldiora traps 9sk in jail, is seldiora not also in jail and unable to make an argument? The past influences the present and the future. If 9sk is dead than seldiora cannot make an argument. His "possibilities" are impossible, and self-contradictory.

As long as seldiora can make an argument, 9sk can always make an argument. Consider seldiora's past helping con within his tournament round 1 debate. If seldiora gives 9sk's arguments ahead of time similar to how he tried to refute Supadudz, even if he forces 9sk to "die" without dying himself (which is absurd to think about), seldiora is still fighting against 9sk in a way, and thus cannot possibly win.

Yes, I may have entrapped myself in multiple time paradoxes, and I admit some of them don't make that much sense, but if you do anyone of these possibilites, 9spaceking does not win, rather both tie. You have completely ignored the possibility of tie-ing the debate. It is not CERTAIN that anyone will vote and it is also not CERTAIN that 9spaceking will by slaughtered by the Mafia.

You think nobody will vote, but is that for certain? Consider the fact if someone managed to clone their past self just to have a debate with their current self, and if the voting period was six months, moderators would at least figure out something was going on and try to find out who really won this debate. It would be indeed suspicious if they had the same IP address or if I mentioned that 9sk is indeed me. Ragnar would without a doubt vote on the topic, and since it's unrated, he wouldn't mind giving his honest opinion who would win. As I have proved in countless contexts seldiora debating the opposite of what he really believes in has horrible backing and was easily tied or defeated by other people, there is no doubt that 9sk would defeat seldiora. Through time paradoxes unable to be resolved, there is zero chance that 9sk would die without seldiora also dying. And even if 9sk couldn't get a round off, seldiora's bad standard set through his tourney 1 debate goes to show 9sk still would have a presence enough to put a dent in seldiora's case and potentially defeat him.

Sure, that is probable, but it isn't certain. What if all the voters got hit by a bus? You are not proving your side, you are not proving that it is certain that 9spaceking will win. You are only proving if it is probable. You have analyzed statistics, and said things about time paradoxes and how Ragnar will vote, but no. The fact that 9spaceking is better than the user seldiora does not mean 9spaceking will certainly win. The time paradoxes are wiping 9spaceking and seldiora from existence, therefore the debate never happened therefore, 9spaceking does not win. If seldiora kills 9spaceking at the very beginning of the debate (when it hasn't started) the debate will be either wiped from existence or fully forfeited as both of them are dead. 

Again 9spaceking does not have the capacity to certainly win. 9spaceking cannot certainly win, there is no such thing as certainly do an action, there are just too many variables. If 9spaceking is killed by the mafia, like I said, even though not probable, 9spaceking can not win (if he full forfeits).