Xi'an Chi Xan Vs Mr. Fantastic
Okay, this is a toughie but it's possible.
We all know Reed Richards. The main thing about Xi'an is that he has one hand that destroys on a molecular level in seconds (works on organic and non-organic). Basically, he touches a chair and it's dust, or a person himself. His other hand heals within seconds. He is also a master at every form of Eastern Martial Arts. He's very quick, agile, etc. He's also a very strong-willed individual and highly intelligent (nowhere near Reed, but definately not Johnny Storm
)
Prep-Time
This will benefit Xi'an. Reed has access to time machines and such but he has no way of knowing that Xi'an is from an alternate future or a means to research him. No one in the main 616 has ever heard of Xi'an. Reed would be going in blind.
Now Xi'an is lucky. The world of 2099 is a bit sketchy of the heroes of the past and even moreso on what became of them, but there was a Fantastic Four 2099 for a short time and it was really Reed Richards from some alternate past. He was dead on the exact same guy with the exact same intelligence. Xi'an knows Reed personally, and Reed has no idea who Xi'an is.
And so, during prep-time Xi'an has time to ponder this, consider everything he knows about Reed, and plan as he meditates. He has his death hand but he wouldn't use it on another human being, so that's out. Thus, he has to consider differant methods. However, being from the very advanced future, I'm sure he can find some basic stuff. The main thing though is that Reed is elastic and I think most people's first instinct there is to freeze it or melt it. Xi'an won't melt him for fear of killing him, but freezing... that's something else.
Now... I can't say I know much about freezing or whatnot, but Xi'an will. The reasoning for this is that during the X-Men 2099 series there are quite a few instances where freezing came up regularly. Cerebra froze 3 of the false X-men to keep them from degenerating and all the X-Men knew about that. Xi'an wasn't with them at the time but did show up during his bad days and stole those X-Men for the Theatre of Pain and took charge of them during his initiation and all that. It seems like frozen cryrogenics is a pretty common thing in the future, so something like that makes me think that someone as resourceful as Xi'an should have no problem finding something that can freeze a person.
Now... come the battle
They are on an Island, which doesn't really benefit or hurt either person. I'm certain Reed will have something whipped up and ready to go but Xi'an isn't going to rush into things. He's very subtle and patient. Very sneaky. He's pretty much a kung fu monk
Xi'an will search for Reed and Reed will search for Xi'an. They will eventually find one another and I'm certain Reed will try a gun of somekind but Xi'an is agile and fast. He was able to dodge punches by Junkpile and leap over his huge frame and such. It'll be hard for Reed to tag Xi'an. However, Reed isn't that quick and his ego is something of a hinderance and I see him relying on his tech to win, but Xi'an is hard to hit, as stated, and if he can manage to get close his hand can break all tech that Reed has.
NOTE - cutting into my stuff here for a random thought... if Reed tries to use the Island's tech to trap Xi'an, Xi'an can just break down his prison and make his way out.
Basically, what it comes down to is Xi'an will use whatever freezing means he has to freeze Reed. Whether it be a gun, caplets like Impact Webbing, a disc that emits the freezing feature... etc. Basically, Xi'an gets close and tags Reed... or from a distance with a distant blaster, and Reed is frozen in place and Xi'an wins.
Final Thought
To make it quick, what makes Xi'an in this is that he actually knows Reed Richards personally. He knows who he is, his mentality, and what he's capable of (whereas Reed's coming in blind). He has 24 hours to plan this out and the freezing option seems best. With the future tech of the 2099 universe it shouldn't be hard to come accross something that can freeze easily. Heck, today we have fire hydrants and such. 100 years from now should have great improvements in that type of thing. Not to mention that Xi'an has a history with cryrogenics, it's very much in character and possible. Then when they meet, it's just a blast and a win.
And not to belittle Reed's tech and planning, but when he doesn't know who he's planning against it isnt' as impressive or Deus Ex Machina-ish. He won't know anything about Xi'an, his powers, his mind, his past, etc. He's blind and Xi'an is coming in fully aware.
And Xi'an's fighting ability, agility, intelligence, and his destruction hand is enough to where if Reed gets a drop on him, he can defend himself until he can get his freezing attack in. And that's only IF Reed gets the drop on him. We can't assume he will.
Winner - Xi'an Chi Xan