- "Fiends. They fall from Sin's body and are left behind in its wake."
- —Lulu explaining to Tidus what Sinspawn are
Sinspawn are creatures born from the gargantuan beast Sin in Final Fantasy X. They are a vital part of Operation Mi'ihen, as the Crusaders use the Sinspawn to call out to Sin, which would inevitably be drawn to them. Five Sinspawn are fought during the course of the game, six if the Sinscale is counted.
Sinspawn are presumably fiends that are formed by outlets of the multitude of pyreflies that composes Sin's physical form. Collectively, the forms of Sinspawn coincide with those of reef-dwelling creatures, such as anemones and jellyfish. This suggests Sin produces some type of sustenance that allows it to act as a living ecosystem.
- Sinscales - A small, weak Sinspawn. First encountered in Dream Zanarkand.
- Sinspawn Ammes - (a large anemone-like creature), fought by Auron and Tidus in Dream Zanarkand.
- Sinspawn Echuilles - (a jellyfish-like beast), fought by Tidus and Wakka in the water following the attack by Sin on the S.S. Liki to Kilika.
- Sinspawn Geneaux - (a shelled plantlike monster with large tentacles), fought by the party at the steps of Kilika Temple.
- Sinspawn Gui - (a large armored arthopodic collative), fought by the party and eventually Seymour during Operation Mi'ihen.
- Sinspawn Genais - (a pallet-swap of Sinspawn Geneaux), fought by the party when fighting Sin (core).
- The Rift Beasts genus from Final Fantasy XIII-2 greatly resembles Sinspawn.
- In Dissidia 012 Final Fantasy, there is a trade material called "Sinspawn". The item's description says "get too close and you'll get dizzy", referring to Sin's toxins.