The easiest way is doing it similarly to an 16x32 tile, but set the offsets so the tiles overlap each other (set the offset to 08 instead of 10).
Remember to set the tilemap to overlap itself so you won't waste space on duplicate (or blank) tiles.
-------------------- <blm> zsnes users are the flatearthers of emulation
Also, I want to make small announcement. I will be "converting" this tutorial to an xkas/asar format once the new text editor for posting is implemented. I already converted a good amount of my first post but editing has become a pain with the current editor that I gave up.
And while I'm at it I will probably fix many errors, add more routines and clarify a few more points. I'll edit this post when I'm done.
First of all, I apologise for the late reply. I haven't been checking this thread often.
Lots of sprites are being spawned probably because the routine that spawns the sprites is running again and again. You should make it run only once using a RAM Address. Set a flag to some non-zero value in the spawning code and prevent the routine from running if said flag is non-zero.
I'm not so good at making sprites, but at least I can make bone-throwing Hammer Bros, giant enemies and (rarely) bosses by simply changing some code. One of my sprites is in the Waiting Sprites Section.
By the way, good tutorial, but I need a video demonstration so I can improve! Thank you very much!