5e Warlock - Pact of the Shen Lung (Celestial Warlock variant)
by Marc SaindonSimply put, the Warlock character makes a pact with a Celestial Dragon (Shen Lung) as a Patron. These dragons aren't in Mystara per se, but can be wedged with a quick retcon, and provided a home on plane of existence that has access to Ochalea. This realm could be the "Plane of Kunlun", a grandiose mountain world, or Kunlun could be Ochalea's Feywild counterpart (if you retcon 4e's Feywild into Mystara, or adapt the Good Kingdom from Tall Tales of the Wee Folk).
Notes:
Shen lung
Kunlun (mythology)
(Image from: https://www.deviantart.com/kydoman/art/Chinese-Dragon-983709371)