Okay, I'm going down the rabbit hole, wish me luck!
An exact copy of yourself is not actually a mirror match. It's actually a symmetry around a point. If you strike out with a sword in your right hand, you will see an oncoming swords coming at you on your left (their right).
Now clearly there's some third party pulling the strings here. Making clones of people, somehow setting up a perfectly symmetric battle where every strike is responded to with its mirror. It almost seems like Moriarty is up to his devilish schemes, trying to break my deductive reasoning skills

Let's examine our assets, shall we?
I have my clothes, my good looks, a full compliment of weapons including swords and guns intended to be used against my clone. I have my clone, if that is an asset.
I have an instinct for survival, so if the clone is anything like me, it has an instinct for survival too. It also would be deducing how to get out of this situation. We think alike, that, could be a valuable asset. But is it really a clone of me? Let's deduce. Key assets: two pairs of hands
Action: Ro Sham Bo. 10 games straight, a tie each time. The clone knows we have a perchance for throwing scissors statistically more often than we should, but has yet to adapt to rocks. 20 games. Now we both have moved to throwing mostly rocks. 30 games. We are indeed clones in every way shape and form.
I make the conscious decision to think not just in terms of the survival of this one body, but to think in terms of our shared survival. My clone naturally does the same. Now I have one fewer opponents, and one more ally.
Suppose you are fighting exact copy of yourself in perfectly balanced arena. Replica is doing same moves as you do. How would you defeat it ?
"It" is a potentially ambiguous antecedent. A lesser man might presume it has to mean defeating my replica, but one with my deductive capacities can easily see through this. At best, only one of us can defeat the other, and it matters not which one. Thus, clearly the antecedent of "it" is not my clone, but the "perfectly balanced arena."
Loophole unlocked.
Smile at myself. Now to defeat this arena's perfection. We need to know where it is. Grab an iron sword and a hammer. Point the sword in a direction, lay it in the ground, and tap it repeatedly with the hammer. Hypothesis: if this is the North-South direction, the sword will magnetize from the taps of the hammer. 10 minutes, no luck. Try 90 degrees from that orientation, no luck. Perhaps sword is not made of iron at all... or....
We're at the magnetic north pole. Of course Moriarty would have to put us at an exotic locale such as that to ensure the direction of earth's magnetic field didn't disrupt the perfection of his trap. His mistake though, for he forgot to think through one final detail.
The north pole is where Santa comes from. Certainly we can devise a way to flag Santa down as he passes for assistance.
So all I have to do is be a good boy... pair of good boys... for 7 days, 3 hours, 27 minutes and 30 seconds. Then Santa will come and bring me the present I always wanted: a 2 year old child a Costco sized container of pixie sticks.
No perfectly organized trap can survive the destructive potential of a 2 year old child, especially when hopped up on sugar. That perfect arena will lose its perfection, and be defeated!
Your move, Moriarty! Next time try to spring your trap when I have less Christmas spirit to use!