The Wind Elementum is found on the Dead Island of Sunfall Shores. Defeating it completes the Breath of Life feat, awarding 15 TP. The newest Elementum is much more powerful than its older counter parts. The weaknesses of the old Elementums have been removed. The Wind Elementum is a real challenge, but nothing we can't handle with a good strategy.
First, you should know a few things about the Elementum. It is immune to Poison, Confuse, and accuracy debuffs, so don't bother trying. Do not debuff any of its stats below 33 or it will buff all of its stats +100. It likes to use Confuse pretty often, so there is some luck involved in the battle. A few well-timed Confuses can destroy any strategy. The upside is that the Wind Elementum tends to miss pretty often, because Confuse only has 50% accuracy. It's most powerful attack, Relentless, misses a good bit as well. Relentless can hit a bunch of times and easily one-shot any Miscrit. This makes buffing your defenses pretty pointless. The Elementum will always poison your Miscrits for 99 turns, but it only does about 6 damage each round. Try to use Miscrits with high Physical attack if you have them at level 30. Elemental Defense is more important than Physical, because the Elementum's Physical attack is pretty much always going to kill you if it hits. And of course, don't bring any Earth Miscrits to this battle.
So, now that we know all of that what do we do? The strategy is fairly simple. Bring only level 30 Miscrits. You need at least one, preferably two, that can debuff -11 to both defenses. You also want Miscrits with strong attacks, because we need to pound this guy fast. Physical attacks do more damage, so bring any strong Physical Miscrits you have (that aren't Earth). Try to bring Miscrits with good Elemental Defense if possible. Also, if you have any level 30 Miscrits with Sleep or Deep Sleep bring them. Start by debuffing the Elementums defenses to -33. Again, do NOT go below that or you will invoke its wrath (+100 to all stats). Next, use Sleep or Deep Sleep if you have it. If you hit it with Sleep, use one Mythical attack buff potion for whichever attack your current Miscrit uses. If you use Deep Sleep buff yourself with two potions instead of one. Next, just start pounding on it with your strongest attack. The Sleep strategy can be repeated with more than one Miscrit, but you do risk missing. If you don't have Sleep, or you don't want to use it, just keep hitting it with your strongest attacks. If it buffs itself with Unbreakable lower its defenses back to -33. When your Miscrit is one normal attack away from death, use a Mythical Heal. Relentless will kill you if it hits a few times, but Whirlwind should do less damage than your heals. The Elementum can be defeated without heals, but using them reduces the risk and increases your chance to win. Mythical Heals are particularly helpful with your last Miscrit if you're close to winning but you know you'll fall a little short.
As I mentioned earlier, Confuse is the biggest weakness of any strategy. If you get hit by Confuse too often or at the wrong times, you will lose. Just dust yourself off and try again. Unless you have terribly bad luck it shouldn't take more than a few tries.
If your Miscrits just can't seem to handle this fight, you can use Lightning Magic to give yourself a boost. Just make sure you use it with a Miscrit with really high Elemental Attack. Be careful though, you don't want to waste it.
Lastly, I will leave you with a great quote about strategy from the book Ender's Game:
“There is no teacher but the enemy. No one but the enemy will tell you what the enemy is going to do. No one but the enemy will ever teach you how to destroy and conquer. Only the enemy shows you where you are weak. Only the enemy tells you where he is strong.” -Mazer Rackham
If you haven't read Ender's Game, I would highly recommend picking up a copy! It's one of my favorite books, and a really great read.