I don't support the sprite sheet right now as I realize separate sprites files are easier to be imported.
Why you need a sprite sheet anyway? which game engine you are using? I have experienced with unity and Game Maker
Viewing post in Skeleton Warriors Pixel Art Monster Asset comments
I'm using Unity. Sprite sheets make sure the sprites are centered each frame. Although I really like your assets, I have to manually center each different animation because they all have different center points - which wastes a lot of time. Providing sprite sheets would help a lot and it would just be more organized in general. I appreciate your work though - keep it up.