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.

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.

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.