At the beginning of your upkeep,
scryTo “scry N” means to look at the top N cards of your library, then put any number of them on the bottom of your library in any order and the rest on top of your library in any order.
If a player is instructed to scry 0, no scry event occurs. Abilities that trigger whenever a player scries won’t trigger.
If multiple players scry at once, each of those players looks at the top cards of their library at the same time. Those players decide in APNAP order (see rule 101.4) where to put those cards, then those cards move at the same time.
An ability that triggers whenever a player scries triggers after the process described in rule 701.22a is complete, even if some or all of those actions were impossible. (CR 701.22) 1.
Whenever you
discardTo discard a card, move it from its owner’s hand to that player’s graveyard.
By default, effects that cause a player to discard a card allow the affected player to choose which card to discard. Some effects, however, require a random discard or allow another player to choose which card is discarded.
If a card is discarded, but an effect causes it to be put into a hidden zone instead of into its owner’s graveyard without being revealed, all values of that card’s characteristics are considered to be undefined. If a card is discarded this way to pay a cost that specifies a characteristic about the discarded card, that cost payment is illegal; the game returns to the moment before the cost was paid (see rule 733, “Handling Illegal Actions”). (CR 701.9) a card, each opponent mills two cards. (They put the top two cards of their library into their graveyard.)