ho in gioco [card]molten-tail masticore[/card] e voglio uccidere l'oppo avendo solo 2 mana, [card]ashnod's altar[/card] e zero carte nel cimitero: posso farcela?
ovvero, posso sacrificare la masticora dopo aver dichiarato l'abilità e pagarla con il mana di altare e poi in risoluzione esiliare proprio la stessa masticora che è andata nel cimitero?
io credo di si, ditemi voi come e perché.

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.

Le cose funzionano esattamente così:
metto in pila l'abilità di ashnod
TOP
ashnod
BOTTOM

Tu vorresti fare:
1- metto in pila l' abilità della masticora
2- metto in pila l' abilità di ashnod

605.3. Activating an activated mana ability follows the rules for activating any other activated ability (see rule 602.2), with the following exceptions:

605.3a A player may activate an activated mana ability whenever he or she has priority, whenever he or she is casting a spell or activating an ability that requires a mana payment, or whenever a rule or effect asks for a mana payment, even if it’s in the middle of casting or resolving a spell or activating or resolving an ability.

605.3b An activated mana ability doesn’t go on the stack, so it can’t be targeted, countered, or otherwise responded to. Rather, it resolves immediately after it is activated. (See rule 405.6c.)