Four decks stack sixteen tableau piles and sixteen foundations with Yukon's free-order group moves, medium difficulty, and a 75% win rate favoring skill.

Quadruple Yukon Solitaire is Yukon Solitaire played with four decks instead of one: sixteen tableau piles and sixteen foundation piles, one set of four suits for every deck. It's medium difficulty, with a 75% chance of winning, and the outcome comes down to skill more than luck.
The rules are identical to Double Yukon Solitaire and Triple Yukon Solitaire; only the deck count and the pile counts change.
If you run into anything odd or have an idea that would make the game better, please contact me.
Enjoy!
16 foundation piles: Build up from Ace to King in the same suit.
16 tableau piles: Alternate-color build down. Groups of cards can be moved in any order. Only a King, or a group of cards led by a King, can fill an empty pile. Each pile starts with more face-down cards than the last, plus five or six face-up cards on top; see the Tableau section below for the exact counts.
There are sixteen foundation piles.
Any of the sixteen foundation piles may be started with an Ace of any suit.
A card can be added to a foundation pile only if it's one rank higher and the same suit as the pile's current top card, so the only card that fits on a 5 of spades is a 6 of spades. There can be no more than 13 cards in a pile.
The top card of each foundation can be moved back into play if another pile will accept it.
Sixteen tableau piles make up the board. The first pile has a single face-up card. Every pile after that carries one more face-down card than the pile before it, then six face-up cards on top - except the last three piles, which get five face-up cards instead of six.
A card can be added to a tableau pile only if it's one rank lower and the opposite color of the pile's current top card, so the only cards that fit on a 9 of clubs are the 8 of hearts and 8 of diamonds.
Cards on the tableau that are not covered by another card are free to be played onto the foundation or any other tableau pile.
Only Kings may fill empty spots in the tableau.
Any face-up card in the tableau may also be moved to another tableau column where it fits, bringing along any cards stacked on top of it, in any order.