This ability, derived from the acidic mist, should be more accurately named as 'Driving Mist' rather than being strictly called acidic mist.
Though it seemed like a pointless combat technique, Xin Yun wasn't disappointed at all. A dragon that can't manipulate clouds—is that even a dragon? Most importantly, both 'Driving Mist' and 'Soaring Clouds', were essential combat techniques in Xin Yun's vision!
The use of 'Driving Mist' was essential for close combat or ground battles, belonging to the lower-tier combat techniques of the Divine Dragon. Even common demons would be proficient in such skills.
However, when it comes to 'Soaring Clouds', that's something only Great Demons, particularly those from the ancestral lineage of dragons who play in the water, could learn. Their ability in 'Soaring Clouds' is incomparable; it's certainly not something ordinary demons can match—this is a matter of capability.