You are capable of producing an invisible, intangible “fog” over a large area. This fog is capable of hijacking the senses of everything inside, living or artificial (like cameras and microphones), giving you the ability to access and override them at will to make them experience whatever illusions you desire, effectively turning the area into a holodeck. You are also capable of creating illusions of the same calibre that can be visible even to people outside the fog, although you will not get to access their senses or be capable of specialising the illusions to specific people like you would if they were inside.
You can range from giving everyone in the fog the same illusion to giving each individual person a different personalised experience, with their expectations and knowledge filling in the gaps for any details about the illusions you don't personally assign (how it breaks, what it looks like on the back, etc.).
Those inside the fog will instinctively act in such a way to maintain the illusions they’re observing (i.e. if they lean against an illusory wall they will unconsciously lean in such a way that they are still balanced and thus won't fall through it), if they push past these instincts and/or make mistakes the illusions automatically adjust to maintain realism and explain away any inconsistencies caused by the illusion in whatever way the subject thinks would make the most sense (i.e. if they tripped and fell through an illusory wall then the illusory wall will have “broken”).
Your power is even capable of hijacking and tricking exotic senses like thinker powers, although they take more focus to understand and manipulate.