Cry of the Carnarium’s power-and-toughness-reducing effect affects only creatures on the battlefield at the time it resolves. Creatures that enter the battlefield later in the turn won’t get -2/-2.

Creatures that would die after getting -2/-2 will still be on the battlefield when cards are exiled from graveyards. They won’t die, and will instead be exiled after Cry of the Carnarium is entirely finished resolving.

Cry of the Carnarium’s replacement effect affects any creature that would die in the turn, even creatures not on the battlefield as it resolves.