The Ruby Mist is a pink-purple mist with faint sparkles. A product of the Phantom Ruby that is created when the gem is used, this mist is able to create distortions in space-time that can warp those who enter it to different locations.
In Sonic Mania, and its expansion Sonic Mania Plus, the Ruby Mist only appears in Titanic Monarch Zone Act 2, as a product of Dr. Eggman's usage of the Phantom Ruby at the time. In gameplay, these mist clouds can be found covering passages, floors, ceilings and so on. When a playable character comes into contact with a mist cloud, they will be warped away, only to be deposited into another location (some of which are only accessible through the Ruby Mist clouds) by another mist cloud. Each Ruby Mist cloud is linked to another one in a specific location, although some multiple mist clouds are linked to one specific.
While the Ruby Mists can be used both ways, the "receiver" mist clouds are often positioned so the player cannot reach them once they have been deposited from them. Also, the Ruby Mist clouds are sometimes arranged such that when the player falls into it by mistake or takes the wrong Ruby Mist-ridden passage, they will be transported back to an earlier point in the Act to try again.
In Sonic Forces, when Infinite used the Phantom Ruby, a pinkish purple aura similar to the Ruby Mist appeared around him.
↑ 1.01.11.2Live Sonic Mania Developer Playthrough (3:46:05). Stealth (20 August 2017). Retrieved on 22 August 2017. “Stealth: So about this Act, eh, Act 2 Ti-titanic Monarch Zone... Uh, the, uh, purple-pinkish mist is actually rub-called Ruby Mist. And it is a product of Eggman using the Phantom Ruby at this moment, which is distorting Titanic Monarch itself.”