Ruin Grinder
Artifact Creature — Construct
Menace
When this creature dies, each player may discard their hand and draw seven cards.
Mountaincycling 
(, Discard this card: Search your library for a Mountain card, reveal it, put it into your hand, then shuffle.)
Hector Ortiz
Commander 2021 (C21)
• #384Rulings
Players decide and announce in turn order, starting with the active player, whether or not they want to discard their hand. Then, all players who chose to do so discard their hands and draw seven cards. Players later in the turn order will know if players before them are discarding, but they don’t get to see what those players will discard to help them decide whether to discard themselves.
(wotc • 2021-04-16)
Rulings
Players decide and announce in turn order, starting with the active player, whether or not they want to discard their hand. Then, all players who chose to do so discard their hands and draw seven cards. Players later in the turn order will know if players before them are discarding, but they don’t get to see what those players will discard to help them decide whether to discard themselves.
(wotc • 2021-04-16)