Skulltaker reads:

Action: When an opponent's unit leaves play, spend 1 resource to attach it facedown to this unit as an experience.

The Unending Horde reads:

If your [Orc] unit would leave play, you can attach it to this card instead (it is not considered to be in play).

Action: Spend X resources to put all [Orc] units attached to this card into play in your battlefield. X is the total printed cost of attached cards. (Limit once per turn.)

An opponent's unit is destroyed/sacrificed.

The opponent's unit leaving play is attached to an Unending Horde instead, so I respond by "skulltaking" it.

Is the opponent able to respond to my "skulltaking" by triggering The Unending Horde's effect and putting back into play the newly attached card?

Yes, the opponent can respond as long as he has the money.

Isn't that a violation of the FAQ that says that a triggered action can only be triggered once per copy of the action and only once per triggering event?

In this example we have: one trigger for both effects and only one action (Horde is a constant). How this break rules?

You are right, I was getting ahead of myself! I was answering the question I thought was being asked and not the actual question. As always, you are the man Virgo!

I don't think that you can trigger the Skulltaker's action in this case, because it reads "when an opponent's unit leaves play ...".

The Unending Horde reads "if your [Orc] unit would leave play". So, instead of leaving play, it is attached to the horde.

No trigger condition for the poor Skulltaker here.

I agree with Virgo and Gnomeschool both

The case of Unending Horde is similar to that of the Dwarf Quest "Reclaim the Hold"; as explained by Lukas in the Rules Summary (mantained at deckbox.org), there's a replacement effect marked by the word "instead", so a unit never really leaves play if it's destroyed, and Skullataker's action cannot be activated (as noticed by Gnomeschool).

However, if a unit is sacrificed, the replacement effect of Undending Horde doesn't work, since the "The act of sacrificing a card cannot be cancelled or prevented by other effects. After a card is sacrificed, it is placed into its owner’s discard pile." (see the FAQs under "sacrifice"); in this case the unit leaves play and can be "captured" by the opponent's Skulltaker if he has enough resources (as Virgo said).

I don't think that you can trigger the Skulltaker's action in this case, because it reads "when an opponent's unit leaves play ...".

The Unending Horde reads "if your [Orc] unit would leave play". So, instead of leaving play, it is attached to the horde.

No trigger condition for the poor Skulltaker here.

Skulltaker is worded funny, I think he should have constant effect instead of the action, because now he is always taking unit out of discard pile: unit dies, his trigger activates, but there is no action window, unit goes to discard pile, he takes the unit (the skull )

I agree with Virgo and Gnomeschool both

The case of Unending Horde is similar to that of the Dwarf Quest "Reclaim the Hold"; as explained by Lukas in the Rules Summary (mantained at deckbox.org), there's a replacement effect marked by the word "instead", so a unit never really leaves play if it's destroyed, and Skullataker's action cannot be activated (as noticed by Gnomeschool).

However, if a unit is sacrificed, the replacement effect of Undending Horde doesn't work, since the "The act of sacrificing a card cannot be cancelled or prevented by other effects. After a card is sacrificed, it is placed into its owner’s discard pile." (see the FAQs under "sacrifice"); in this case the unit leaves play and can be "captured" by the opponent's Skulltaker if he has enough resources (as Virgo said).

Right, constant kicks in faster and no trigger for Skulltaker. Also: sacrifice cannot be prevented but the destination of sacrficied unit can -> unending horde works.

Right, constant kicks in faster and no trigger for Skulltaker. Also: sacrifice cannot be prevented but the destination of sacrficied unit can -> unending horde works.

"No, once you sacrifice the unit, you cannot stop it from entering the discard pile unless a card text very specifically overrules this by referring to the term "sacrifice". (Lukas Litzsinger)

The way i read the above statement, a sacrifice can't be prevented nor its destination can be changed (the discard pile)... however, since English is not my native language, i may be totally wrong

EDIT: Correction - there's also the similar effect of Volkmar the Grim; in this case, as explained in the FAQ, a sacrificed or destroyed unit is placed on the bottom of its owner's deck. However, Volkmar's text is a bit different, since it says "If a unit would enter its owner’s discard pile ".

Horde does exactly that, don't quote me answers from 2 years ago when instead effects didn't even exist.

Ops, sorry, i've made a correction in my post above

Skulltaker is worded funny, I think he should have constant effect instead of the action, because now he is always taking unit out of discard pile: unit dies, his trigger activates, but there is no action window, unit goes to discard pile, he takes the unit (the skull )

What's the problem with taking it from the discard pile? i think the situation between Skulltaker vs. Unending Horde or Volkmar is easier to understand like it is at the moment.

Skulltaker is an replace effect just like the Horde, but he actually doesn't prevent unit from entering discard pile (Hekarti triggers and all leaves play/enter discard pile effects too).

You mean it should be a replace effect?

Because at the moment it isn't really, but I think it works fine this way.

Thank you all for the answers. This is a really interesting discussion.

Poor Skulltaker

But more importantly I have learned that one cannot attached sacrificed units to The Unending Horde. This changes a lot!

You can, lol.

Horde specifically says that it changes destination for cards that would leave play, sacrifice is one of the ways a unit leaves play.

Okay I thought that although The Unending Horde does refer to cards leaving play, the card does not specifically refer to the term "sacrifice ."

But in any case, sacrifice means to remove a card you control from play and this is the act that cannot be prevented. So I guess where it ends up is no big deal, as long as it left play.

Thanks again!