These are instructions for creating custom sprites.

First, take your sprite picture and place it in the SMTC/Custom/Sprites folder.

Next, edit the SpriteDefs.scp file and add your sprite's EXACT name to the end
of the list.  This does not include the type, so Arrow.bmp would be added as
Arrow.  The list is not case sensitive.

Now, the sprite has been defined and will be loaded into SMTC at startup.

Next, you must add the lines to spawn the sprite in a room.  Go to the scripts
directory and then Rooms, and open/create your room script.  Put in a line
called
Sprite("MySprite", "SpriteIMade", 20, 20, 0, -1) replacing SpriteIMade with the
exact name you assigned to the sprite (an example is Rain, one of the sprites
already inside the folder)
Now, your sprite will just be floating in midair at (20,20) in the room.  You
can change the coordinates to something more suitable if that part of the room
is invisible.  Press D once, and look at the LFT and TOP values in the bottom
left.  Those are Samus' current position, so pick something around there to put
your sprite at.  Admire it!

To make your sprite do interesting things, you must use
ModSprite("MySprite", -1, -1, 1, 0, 0, 0, 0, 0)
Those extra zeroes are for enhanced physics, like gravity.  Alternately, you can
use
SpecialSprite("MySprite", 1)
This makes the sprite fall to the ground and sit there.  It obeys clipping
bounds and will not move until terminated.