Ghost bloons are too small to be easily hit, as well as 10M health being prohibitive, unless they nerf the bloon for this game of course. There is already a ghost boss (not a bloon) in BSM2 mobile on round 60.
A special upgrade: The plasma tentacle now can remove all special features it touches. MOAB class bloons are unaffected. This means that regen bloons forever lose that property. Plus other affected bloons.