Tip: Layer 3 backgrounds and tides disappear when you hit a message box, so plan your level around that. For example, you can add a sublevel without layer 3 at the start/midpoint, and include your message there.
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Details for Vertical Boo Stream, horizontal wave movement
SMW Sprites - Vertical Boo Stream, horizontal wave movement
It's a Boo Steam that moves up/down with Left/Right Wave motion.
On Extra Bit Set it'll initially start moving right, otherwise it initially moves left.
It also uses first property byte for custom intitial Y speed (By default, it "Faces" Mario). More info in ASM.
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