Dandasuka

 As a stat block, a dandasuka makes for a great spy or scout. As a storytelling device, a dandasuka is a minor disaster waiting to blow. While you can use them as plain antagonists, i feel like the best dandasuka stories would be those where a dandasuka ends up in the PCs service, be it as a dandasuka's own nefarious plan, or due to the PCs foolish megalomania.

An old cleric, who is a retired adventurer, tutors the king's only son. After a summer at his uncle's palace, the child is completely changed - prone to violent and chaotic outbursts, easy to go in a rage and highly unpredictable. Gathering his old crew for one last mission, the cleric discovers the boy has been replaced with a dandasuka - and his uncle with a Raja. Further investigation shows a deeply entrenched rakshasa conspiracy to replace the entire royal court.
While cleansing it must be done, the old adventurers realize any of their potential allies can secretly be nefarious shapeshifters. 

For his services to the Dark Lord, an aspiring Asmodean Hellknight is granted a highly unusual familiar - a dandasuka. While most knights get obedient imps, drawn directly from one of the nine hells, the young knight has shown a spark of greatness - and his higher-ups reward it by testing him to his limits. The overeager, bloodthirsty fiend is meant to be a lesson in control and restraint, and if the inexperienced knight can fully exert his will over its, he is sure to be inducted into the inner circle of the church. Of course, if he fails, that is one more soul to fuel the forge of hells...

Sir Altos, a champion of The Lord of Second Chances, has found a way to separate fiends from their evil natures and grant them free will. To that end, he has reluctantly agreed to let a free-willed dandasuka join him and his comrades on their travels through the Sleeping Valley. While the dandasuka has managed to put up an appearance of meekness and redemption in front of the champion, when they lay asleep, it has been whispering tales of lost knowledge and hidden powers to the wizard, already the least committed of the group