Slot of platform sprite that Yoshi is on. Does not apply to every platform sprite, for example it does for Pinwheels, Chomp Rock, Poochy, Flatbed Ferries, etc, but not for Hint Blocks, Donut Lifts, etc.
Where the water line starts for sprite physics
Only used for BG3 tilesets $13 (value $07B0) and $1D ($0700)
Value is left at $4000 when disabled
This doesn't affect regular water objects, only hardcoded water for certain BG3 tilesets.
ss = vertical screen number
yy = Y-position of water line