No, Stifle cant target turning the disguised creature face-up, as this isnt an activated ability or triggered ability
For high-value cards, buy already-slabbed copies from PSA, BGS, or CGC where the card has been professionally authenticated
Your opponent certainly needs to change their gameplan if they face it
Included are three complete 60-card decks, each themed around a popular Pokmon
As far as strategy goes it is very important to move Darkrai from your hand to your bench when you need the have a possibility of the defending Pokemon not attacking, also I would definitely play Dark Slumber right away to make the defending Pokemon asleep and then use Dark Resolve especially if the defending Pokemon is asleep and it should be because of Dark Slumber
Add 162 reverse holofoils and the Trainer Gallery subset and you're well past 400 cards total