Mi-a venit o idee si as vrea sa stiu daca functioneaza.

Am pe battlefield Monastery Mentor apoi castez Collateral Damage care are ca si cost sacrificarea unei creaturi.

Acum neclaritatea mea e: merge sa sacrific Monk-ul care iese de la cast pentru cost-ul de la Collateral Damage ?

Nu merge. As an additional cost to cast >> sacrifice. Mentorul zice - when you cast. Sa astepti si o parere mai documentata dar la o simpla citire a celor doua carti reiese clar ca Collateral Damage se casteaza doar dupa sacrifice.
In principiu ca sa poti casta cartea trebuie sa alegi o creatura pe care vrei sa o sacrifici inainte de a pune Collateral Damage pe stack.

nope:
http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=391811
"11/24/2014 You must sacrifice exactly one creature to cast this spell; you can’t cast it without sacrificing a creature, and you can’t sacrifice additional creatures."

deci fara sa sacrifi o creatura nici nu poti sa castezi spellul -> no trigger

ok merci, ii clear acum :) ar fi fost prea fain.

Asta e unul dintre scenarii care necesita sa intelegi cum se casteaza un spell. Includ aici partile relevante:

601.2a The player announces that he or she is casting the spell. That card (or that copy of a card) moves from where it is to the stack. It becomes the topmost object on the stack. It has all the characteristics of the card (or the copy of a card) associated with it, and that player becomes its controller. The spell remains on the stack until it's countered, it resolves, or an effect moves it elsewhere.
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601.2e The player determines the total cost of the spell. Usually this is just the mana cost. Some spells have additional or alternative costs. Some effects may increase or reduce the cost to pay, or may provide other alternative costs. Costs may include paying mana, tapping permanents, sacrificing permanents, discarding cards, and so on. The total cost is the mana cost or alternative cost (as determined in rule 601.2b), plus all additional costs and cost increases, and minus all cost reductions. If the mana component of the total cost is reduced to nothing by cost reduction effects, it is considered to be 0. It can't be reduced to less than 0. Once the total cost is determined, any effects that directly affect the total cost are applied. Then the resulting total cost becomes "locked in." If effects would change the total cost after this time, they have no effect.
601.2f If the total cost includes a mana payment, the player then has a chance to activate mana abilities (see rule 605, "Mana Abilities"). Mana abilities must be activated before costs are paid.
601.2g The player pays the total cost in any order. Partial payments are not allowed. Unpayable costs can't be paid.
601.2h Once the steps described in 601.2a–g are completed, the spell becomes cast.[color=red] Any abilities that trigger when a spell is cast or put onto the stack trigger at this time.[/color] If the spell's controller had priority before casting it, he or she gets priority.

Deci: se vede ca abilitatile care se activeaza la castarea unui spell nu se pun pe stack doar dupa ce costul total a fost platit inclusiv costurile aditionale (highlighted in bold).