Although some people shuffle the packs together when using more than one tarot deck in a reading, I’ve never found that approach particularly easy or effective due to inconsistent card size, thickness and finish. So I have always shuffled the decks separately for any multi-deck spread, usually placing them in different rows, columns or “chains” of the layout. That works well enough, but I decided to dream up a technique to “mix-and-match” the decks in a way that intersperses them similar to shuffling them together while also keeping some of the “mystique” of random selection. Three decks seemed to be the optimum number for this experiment.
Shuffle the packs and set them side-by-side on the table. Take any three coins (I used pennies as implied in the title), shake them in your hand or in a dice cup and toss them onto the table. (You can also flip them or spin them individually in sets of three although it’s a bit slower.) If you come up with one “head” and two “tails,” draw a card from the deck on the far left and place it in the spread. With two “heads” and one “tail,” pull the card from the middle deck. Three “heads” or three “tails” will show the far-right deck to be the source. Repeat this as many times as necessary to populate all of the positions. If you get a duplicate card, you can either keep pulling for that position or treat it as reinforcement.
It’s probably best to use decks that have some commonality (such as three different editions of the Waite-Smith tarot); here I show three Thoth-based decks: the 1983 “three-Magus” version of the original Thoth; Liber T: Tarot of Stars Eternal and Navigator’s Tarot of the Mystic SEA. (Note how challenging it would be to attempt shuffling them together.)