Pathfinder question, DC15 fortitude save but constitution based. what does that mean?

There are two answers: one is a basic answer meant for newer players, the second is an advanced answer based on players with more game experience. I'm afraid I need more clarification which you need to refine my answers to be correct.

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Basic Answer:

The DC for the effect is 15, you roll a d20 and add your fortitude save.

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Advanced answer:

That does sound weird.

Fortitude is Constitution based anyway, so I don't see why the text doubles down on that. Could you give the rest of the text of the ability/spell? Or at least a book and page reference.

Nope just grow up and get about four hundred and fifty thousand pounds and you'll be good

it means that you got ****** in the asshole by a big black dude