From the official release announcement - "Make your own luck with High Stakes skins":
"Pick a card, any card.
Stack the deck with Ace of Spades Ezreal, Queen of Diamonds Syndra, King of Clubs Mordekaiser, and Wild Card Shaco, now joining Jack of Hearts Twisted Fate in the League store and wherever luck is made, not found.
Grab each skin for 750 RP (except Jack of Hearts TF, he’s still 520 RP) or go all-in with the High Stakes bundle at 25% off - that’s 2638 RP or 5651 RP if you need the champs - from now until 11:59 PDT May 25."
King of Clubs Mordekaiser, Queen of Diamonds Syndra, and Wild Card Shaco use this version:
Ace of Spades Ezreal and Jack of Hearts Twisted Fate use a flipped version so it better fits in their champion pages:
[Note: This splash also depicts the previously released Jack of Hearts Twisted Fate, who will now use it and has an updated loading screen slice.]