Well, it looks like a tiny fragment of the shed remained attached to the tip of his tail. On two or three successive occasions. Such that the posterior most short section of the tip of his tail has lost blood flow, died, and will soon drop off. Not an unheard of situation. Won't interfere with a happy healthy life.
Always examine him carefully after a shed, while he's so small and difficult to inspect, to make sure every last shred of shed is free and detached.
Nice moist hides in which to pass the pre-shed period will usually prevent these or similar situations.