Diamond Core of Koa'ki Meiru was a new addition to Duel Links recently from the Revolution Beginning main box, which has actually dramatically improved the stability of Koa'ki Meirus.

They went from an archetype that struggles to stay on the field, to one that goes all-in to OTK, just because of this one card. I know I'm not the only one who thinks that this card is so hard to deal with, but let's see if we can figure out make the most of its usage, and also on the flip side, how to counter it.

Since this card basically gives you one free turn by protecting ALL your Koa'kis from their maintenance cost, you have to be sure that you'll win that turn, and if not, survive the next turn. This means that you'll need to survive until you get a good hand, which may require you to pass on a dead hand. Because of that, this deck really has one mode: OTK.

Here are some tips:

• If you run Hey, Trunade!, try to use it early to return to the hand all non-chainable face-down backrow (like Wall of Disruption, Drowning Mirror Force, etc) or force the wrong timing on chainable face-down backrow (like Enemy Controller, Vampire Takeover, etc).
  
  Or, if Silent Magician could negate it, use Diamond Core early and then use Hey, Trunade! to get rid of pesky backrow. This is OK since you can still banish Diamond Core from the GY for its protection effect. Or, if you're feeling frisky, try to destroy Silent Magician with Maximus first, and then use Diamond Core.
  
  
• You can run the Sealed Tombs skill, which helps in matchups against Koa'ki Meiru, Spellbook, and Vampire decks; for that turn where you go all-in:
  Koa'ki Meiru won't be able to banish Diamond Core for protection.
  Spellbooks can't make use of Spellbook of Fate.
  Vampires can't summon from the GY.
  
  
• If you frequently have bad hands (and your deck is actually built well), Sphere Kuriboh helps when you have to go first. Just pass until you get a good hand, warding off big attacks, and if needed, set some backrow for the opponent to get distracted by.

Well, there are multiple ways to combat Diamond Core. Let's consider what it does; it searches from the deck, and then in the GY, you can banish it for protection of all your Koa'kis from all destruction, period.

Here are a few decent direct solutions:

• You can use Mistaken Arrest in a chain to it to prevent the search, and Sealed Tombs early to prevent the banish. However, the former is not really that useful in the meta yet, as it does affect you as well, and it's too situational right now.
  
  Also, Necrovalley, which was in the new selection main box recently, will be a nice alternative to Sealed Tombs.

Sadly, the search is probably the more important part of the effect, and there is no good, coherent solution (that can be made into a complete deck) other than direct negation via Silent Magician plus prevention of banishing via Necrovalley, as far as I can tell. Who knows, maybe it means that "Gravekeeper" monsters (which are Spellcasters and can be tributed for Silent Magician) can make a comeback? Not likely though.

That being said, a workaround that isn't just countering one specific deck is that you could also just negate all of your opponent's monster effects on the field so that your opponent has to rely on attacking (if they even can).

Therefore, some cheeky solutions are Buster Blader, the Dragon Destroyer Swordsman with DNA Surgery, and Destiny HERO - Plasma.

Buster Blader will at least be able to ward off the primary threat, which is Koa'ki Meiru Maximus, a Dragon. None of the other Koa'kis can attack over it or destroy it by their monster effects (except for potentially Koa'ki Meiru Ice). If you have DNA Surgery, it's generally game as ALL of your opponent's monsters will be useless. This is probably the better solution, as you can build a full deck around Buster Blader.

On the other hand, Plasma is purely a tech card and probably won't work as well as you'd have to draw it AND go second, which are generally best-case scenarios anyways.

I think that ultimately, I do appreciate that Koa'ki Meirus finally have a complete set of cards that make them top-tier.

However, I do expect eventually (maybe in 3 months) that this card, or Iron Core of Koa'ki Meiru,  will be semi-limited, in a similar vein to Amazoness Princess and Vision HERO - Vyon, due to how consistent the deck type has become lately. Maximus could potentially also be limited, but let's not get our hopes up.

Anyways, I hope this has helped you guys learn more about Diamond Core and how you could use it, or if you've been seeing too much of it, how you can counter it. Until next time!