The Raven Man

At the beginning of each end step, if a player discarded a card this turn, create a 1/1 black Bird creature token with flying and "This token can't block."
{3}{B}, {T}: Each opponent discards a card. Activate only as a sorcery.

Dominaria United Promos

Dominaria United

At the beginning of each end step, if a player discarded a card this turn, create a 1/1 black Bird creature token with flying and "This creature can't block."
{3}{B}, {T}: Each opponent discards a card. Activate only as a sorcery.

The Raven Man's first ability triggers at the beginning of each player's end step as long as at least one player has discarded a card this turn. It only triggers once, not once for each card discarded or once for each player that discarded a card. It will trigger even if its controller is the one that discarded a card this turn.