The change log says:
Retribution reworked - now reduces opponents stock by one for each undead in his hand (max 6)
However the card description is still:
Retribution
Holy.
Each player's stock lowered by #Undead cards in his or hers hand (4 max)
It should be:
Retribution
Holy.
Opponent's stock lowered by #Undead cards in his hand (6 max)