Story Archive. War of the Spark. Ravnica Allegiance. Ravnica. Children of the Nameless. Vivien Reid. Core Set 2019. Dominaria. Ixalan. Amonkhet. Kaladesh.
(Tags are for the stories within and do not necessarily represent all stories) 10/11/ 19, Adult, Magical Gender Change, Completed Story star. Trouble With Horns.
Fictionmania is a big free story archive (34050 stories), 3057 with images. Transgender / TV / CD / TG / crossdress / transformation stories. Most of the stories center Magical, SciFi Gender Changes and General Crossdressing Themes. However I do not find fictional stories about adults engaged in sexual acts, bondage.
The Magic Story Archive on the main website helps, but it's not exactly a 'how to'. There have been official attempts at articles designed to catch.
You already KNOW we love us a good story with some complex mythology— maybe some dark magic, and a story that ties everything together.