Can a sacrifice be used to pay for more than one effect? [duplicate]

Question

Someone tried to play the following combo in a game I was in. I think it is an illegal play, so I wanted some help to clarify the rules.

The cards were:

1) Launch Party - "As an additional cost to cast Launch Party, sacrifice a creature."

2) Mogg Fanatic - "Sacrifice Mogg Fanatic: Mogg Fanatic deals 1 damage to target creature or player."

The other player played Launch Party and wanted to sacrifice Mogg Fanatic to pay Launch Party's cost. However, they also wanted to benefit from Mogg Fanatic's own ability.

This doesn't seem legitimate, because it would be a "two for one" (pay one cost, get two spells). Am I correct?

Answer 1

You're absolutely correct: you can only sacrifice the Mogg Fanatic to pay the cost for one of those two effects, not both. From the Comprehensive Rules:

117.10. Each payment of a cost applies to only one spell, ability, or effect. For example, a player can't sacrifice just one creature to activate the activated abilities of two permanents that each require sacrificing a creature as a cost. Also, the resolution of a spell or ability doesn't pay another spell or ability's cost, even if part of its effect is doing the same thing the other cost asks for.

Answer 2

The key part is that these sacrifices are costs. Since you realise this, it becomes quite simple.

You can't pay for two $1 products with the same dollar.

You can't pay for two costs using the same mana.

You can't pay for two costs using the same sacrifice.

CR 117.10 reminds you that nothing allows you to reuse a payment you previously payed.

117.10. Each payment of a cost applies to only one spell, ability, or effect. For example, a player can't sacrifice just one creature to activate the activated abilities of two permanents that each require sacrificing a creature as a cost. Also, the resolution of a spell or ability doesn't pay another spell or ability's cost, even if part of its effect is doing the same thing the other cost asks for.