Strong Buy
Grading Mega Darkrai ex #116 from Pitch Black currently looks like a clear win. At $138.56 raw against $829.99 for a PSA 10, that works out to 263% ROG. Centering is usually the limiting factor on cards like this — check it carefully before sending.
Most grading maths asks you to guess your odds of a PSA 10 first. This works backwards from the prices instead and tells you what those odds would have to be.
The number is different on every card. It's how confident you'd need to be that this copy gems before grading pays for itself, so 20% means roughly a 1 in 5 shot and 50% means a coin flip.
Grade it if you rate your copy better than that, leave it raw if you don't.
It assumes a 9 is the worst you'll get. Centering and edge whitening send plenty of modern cards back at 8 or lower, and that's not priced in here, so treat this as the floor of the bar rather than the whole of it. Selling fees aren't counted either.
(cost - PSA 9) ÷ (PSA 10 - PSA 9)
Pays off even at PSA 9
A PSA 9 alone ($295.00) already covers your $228.56 cost (raw + grading + shipping), so you don't need the 10 to come out ahead.
Anything from a 9 upwards puts you ahead, and a 10 would net you $601.43. The only real risk left is the card grading below a 9.
Among the 51 cards in Pitch Black with PSA 10 sale data, Mega Darkrai ex ranks 3rd for Return on Grading and 2nd by PSA 10 price. Of the 6 Special Illustration Rare cards with PSA 10 sales, it is 2nd for Return on Grading. The median PSA 10 in this set sells for $35.88. 6 of the 51 clear a 100% Return on Grading.