In particular I'm looking at the new Ravnica Allegiance card Shimmer of Possibility. It seems really difficult to randomize the order of a small number of cards and be provably certain neither player knows the result. Is there a procedure to do so that doesn't require removing the cards from sight or involving a neutral third party?
I realize virtually every opponent will be satisfied with a quick scramble; this is a mostly academic question, but there must be a reason the card doesn't let you choose the order.
Using a "random order" implies that the order must not be known to any player, not even to the player controlling Shimmer of Possibility (see also C.R. 701.19a). Thus, it will not do to simply assign a number to each card, then choose a random number assigned this way, then choose the card with that number (for example, to flip a coin if two cards are involved).
This issue occurs, in general, with any effect in which two or more, but a potentially small number of, cards are to be put somewhere in a random order, notably cascade (review C.R. 702.84a). A similar issue is discussed in this thread and this thread.
I realize virtually every opponent will be satisfied with a quick scramble; this is a mostly academic question, but there must be a reason the card doesn't let you choose the order.
This issue occurs, in general, with any effect in which two or more, but a potentially small number of, cards are to be put somewhere in a random order, notably cascade (review C.R. 702.84a). A similar issue is discussed in this thread and this thread.