In the D&D5e rules it indicates that ritually bathing in the blood of dragons can transform someone into a half-dragon. While very few people know the ritual required, many have heard of this process and there are those that seek it out without the full knowledge.
And dragon blood is indeed a potent fluid that brings about great changes. Those who don’t use the proper ritual still emerge transformed by the experience. This two-page table can be rolled on whenever someone is covered in dragon blood, drinks it, or attempts the ritual incorrectly. I would restrict it to dragon blood coming from dragons of adult age or older, and probably only if the dragon was slain in the process.
Download the PDF [here].
(Source: Dyson’s Dodecahedron)