As it has already become known, in season 5, the Mind Flayer will have two forms. The first is his true (shadow) form and the second is his "avatar". Judging by the concept art, his avatar will be very similar to the Spider Monster from season 3. And here the question is whether it will be his old resurrected body or a new one. I am more inclined to the first theory, since in season 3, the Mind Flayer needed a lot of time to infect several dozen people with his particles. Although, given that the gap between seasons 4 and 5 will be at least 1 year, it is possible that during this year the Shadow Monster will have time to infect enough people.