Nice find!
So when looking at what to add to the list, being viable in the endgame is one component. Another component is utility to endgame players, who have access to all the options, and can forego lower rarity options if they have something better. For our purposes, “something better” excludes mythic troops, which are in many cases not practical for even late gamers to have all of the options available.
My point, is in looking for variants of your use of Mist Stalker to take advantage of dervish loops, I stumbled on a potentially even nastier variant that would make Mist Stalker obsolete. This beastie is one of three troops in the entire game with undead-monster dual typing (+4 magic per extra turn!), and also does true damage to boot:
Did you give it a spin in your testing?