I'm bumping this because of Worlds. I posted this on the TCGO Forums page. Slightly modified)
Before reading this post, please review or learn from another site what permutations and combinations are, and you should know basic probability.
We have seen in Worlds that Talonflame's use has been limited to...
Greninja decks. I have not seen them in any other matches, and I don't see any decklists that have Talonflame.
The new Talonflame from Steam Siege allows you to play the Stage 2, free-retreat, one-energy attacker down as your facedown active Pokemon - not on the bench, no use if it is picked up in Mulligan.
The opening hand has 7 cards, pulled from a 60 card deck: 60C7 = 386,206,920 different combinations. EXCEPT that some of those cards are duplicates obviously (2 BREAKS, 4 Frogadier, 4 Greninjas either as 1-3 or 2-2, energies, etc) and you have 4 Talonflame in the deck.
We don't care, believe it or not - it is still 386.2 million combinations possible. Cool!
How many combinations have at least 1 Talonflame, considering we have either 0, 1, 2, 3, or 4 Talonflame?
The answer is...not as simple as I (and the original posters) originally posted. It actually depends on how many basics you have aside from Talonflame.
For 2 non-Talobasics (2 Froakies) - About 177 million give Mulligans. Another 54.8 million more give non-Talonflame starts. About 29 million give Talonflame + 1 other starter. 122 million give you one Talonflame, and the rest of the cards not playable. (This leads to an unfortunate situation where you could land your 2 Froakie in the prize cards, which you don't want.)
But ignoring Mulligans because you reshuffle your deck, you have 209 million combinations that I count for the stats.
About 1 in 4 - 26.2% chance of all 4 Talonflame being dead-weight in a deck.
BUT, if it works, you have a chance to set up Froakie, you have free-retreat, you have a chance to pick off a REALLY weak basic AND pick up any 2 cards you need (And then have them N'd next turn
)
It is still better than having any other basic in the deck, where they might go out in play, and give you a dead hand with something cruddy like Regice, or Articuno, or worse - a free 2-prize hit off of Shaymin
(Can anyone with a better understanding of probability confirm that I didn't oversimplify by ignoring duplicates in the deck?)
I actually have a GoogleSheet that will show you the hard numbers.
https://drive.google.com/open?id=1qEpLS7HleRsHqCSMYQoFdmuklYMNtei5jYwR9BiM-ZE If I'm allowed to link.
HOWEVER, because I actually calculated this, I'd like to post it as an article, be a featured article of the month or whatever, and get a booster box, if people think it's good.