Forgetting reality through these fics

Fics that are so good, I forget where I am. Perfect for escapism or just getting lost in a fantastic story. Forget sleep, I can survive on these fics alone because wow. Good characterization, good plot, typically several chapters (though not always finished), and usually lots of worldbuilding. Seriously, how are these better than some of my favorite books?
(Open, Moderated)
Random works
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The Immortal and the Revenant by RileyWilliamsJr
Fandoms: Harry Potter - J. K. Rowling, Merlin (TV)
18 Apr 2020
Tags
Summary
As usual, Merlin has utterly failed in keeping a low profile by inadvertently getting himself dragged into a mess of a situation that appears to have something to do with a seemingly unkillable snake man, a toad woman, an order of phoenixes, and a boy named Harry Potter who, he quickly finds, is equally bemused by his current predicament. When he discovers how lost the boy is, he resolves to help him and his friends get rid of this dark lord--as well as their malignant (and worse, ineffectual) new teacher.
Translation by EstherM available on AO3 and at: https://www.lofter.com/front/blog/collection/share?collectionId=16968473