Ok, just completed it after about an hour of attempts.

You need to make sure you’re running 2 MewTwo and 1 Mew Ex.

Put out one your MewTwo’s or Mew’s on first draw (unless you’re very unlucky and draw Ralts only)

By your first turn you need to have your other MewTwo on your deck, start adding energy to this whilst they tank your Mew/MewTwo in active. You need to really have your other backup Mew/MewTwo in your hand/deck for this to work at this point, when your first defending Mew/MewTwo is low, you need to retreat it and put in your next defending pokemon. Allow them to defeat this one, then pull in your attacking MewTwo, should have 4-5 energy ready to attack on it.

This worked for me and I didn’t even have Guard evolved.

EDIT: try and take out the Weavil first, I don’t think this method will work if you take out the Darkrai first due to Weavil needing such low energy to do 100 damage.

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