i'm almost sure this is what you need. set backsave to 1 and transparency to 1 or 0
Quote: "
SET SPRITE
This command will set whether the specified sprite restores its background and whether background
transparency is ignored. If the backsave state is set to zero, the sprite will not restore its background and
leave a trail as it moves. If the transparency state is set to zero, the sprite will not treat black as a
transparent color. A transparent color in the sprite image does not write to the screen. If this feature is
disabled, the sprite would appear as though drawn inside a black rectangle where transparency had
previously been used. Both states are set to one as these are the most common settings. If you set the
backsave state to zero, it is your responsibility to clear or paste the background each time the sprite is
moved or animated. The sprite number should be specified using an integer value. The backsave and
transparency states should be specified as either zero or one.
SYNTAX
SET SPRITE Sprite Number, Backsave, Transparency
"
