I remember that Ember and Spike were saved by a mysterious creature. And later, Spike because a female dragon by it.

Much appreciative if anybody find this story thank you

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https://www.fimfiction.net/story/399128/spike-the-succubus perhaps?

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No, sorry.

7827882
https://www.fimfiction.net/story/340438/spike-the-horny-dragoness
? Not many dragon gender change ones...
https://www.fimfiction.net/story/416104/one-for-all
or i think there was one where she summoned spike to a dominance match. vs like garble i think? he wins and turns garble female.. then he gets turned female by backlash or something... but i think thats part of an anthology of stories and i can't find it...

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The front cover have this creature in the center

This is the only image I can find