There's still the question (unless it was answered and I forgot) of how a human manage to get into the dream world in the first place to start all this, so someone may be behind that.
@hanchobakery
fyi: I read "「幻界」が庭の夢魔" as "(「幻界」が庭) の夢魔" ("the nightmare for whom the dream world is its yard", which makes more sense) instead of "「幻界」が(庭の夢魔)" (which, as you mention, makes a lot less sense but is the more obvious/easier way to read that sentence).