Playing Undead Alchemist.

Hey people, long time no seeing you! I've got a question for you.

What would happen if multiple Undead Alchemist are on the battlefield? Assuming, of course, that a Zombie deals damage while they are on the field.

What I suppose that would happen is: let's say a Diregraf Ghoul deals damage to my opponent while I control two Alchemists. Am I right assuming that:

a) Their effects activate at the same time, so I can choose which one to activate first.
b) Their effects are put in stock, so my opponent, once the abilities stop resolving, would discard from the top of his deck 4 cards and put as many zombie tokens as creature cards are put into his/her graveyard (which are exiled).

Your thoughts?

Nope, you're not right assuming that. You'll still only mill 2 cards, however you'll get two Zombies for each creature card milled.

I see. Just so I can explain it better to my MTG community, would you please tell me why it works like that?

Undead Alchemist's first abiltiy is a replacement effect - that is, it replaces one event (A Zombie you control dealing combat damage to a player) with something else (milling that player for that much). When you have multiple replacement effects tring to replace the same event, the affected player chooses the order to apply them in. In this case, once one has applied, the other no longer applies, since no damage is being dealt anymore. So if a Zombie is dealing 2 damage, then one Alchemist replaces that with milling 2. No damage is being dealt any more, so the second Alchemist doesn't do anything.

The second ability is a triggered ability that triggers whenever a creature card is put into an opponent's graveyard from their library. When that happens, both Alchemists trigger and their abilities go on the stack. The first to resolves exiles that card and gives you a Zombie. Then the second resolves, and does as much as possible - it can't exile the card, but you still get your Zombie (since there's no "If you do" clause in there).