There is a bug in Reality Boy when using objects and scrolling backgrounds that put said objects off screen.
I’ve put together a small demo to illustrate this, “manwithball” (source included).
To see the bug, just start the demo and walk straight down. In RB, the ball stays in area 1 (like you would expect actually), but on HW the ball strangely wraps around and shows up again in area 3…
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