On Worlds and Crossover:
In Flex we are presented with at least seven worlds or diegetic spaces, separated by time or by levels of representation:
1) The world Flex lives in, which he calls "the real world." This is also the world of the "Dungeon of Adult Superheroes," Harry, and the Hoaxer.
2) The world Wally-as-adult lives in
3) The textual world of Wally's childhood creations, Flex's former world.
4) The world of Wally as a child
5) The "ceramic world," the goldfish bowl
6) The world (or "polyverse") of the Legion of Legions.
7) The "prison" of Wally as a teenager
...of course, as soon as these discrete worlds are presented, they immediately begin mixing, merging, "crossing over," until by the end they are subsumed into the space of "total reality."
On Panels and Transitions: Flex and Understanding Comics