If a Zombie you control would deal combat damage to a player, instead that player puts that many cards from the top of their library into their graveyard.
Whenever a creature card is put into an opponent's graveyard from their library, exile that card and create a 2/2 black Zombie creature token.
9/22/2011 If you control multiple Undead Alchemists, the multiple replacement abilities will have no added effect. Combat damage dealt to a player by a Zombie you control will be replaced only once with cards being put into that player’s graveyard.
9/22/2011 Whenever a creature card is put into an opponent’s graveyard from their library, the triggered ability of each Undead Alchemist you control will trigger. The first such ability to resolve will exile that creature card and create a Zombie token. Subsequent abilities won’t exile the creature card, but each will create another Zombie token.