This is the 32x32 Spiny boss used in the first castle of SMWCP1.
It will attack Mario by spinning around the room or by stopping to shoot fire at him. Every 3 attacks, a Throw Block will drop from the ceiling, which can be used to hurt the boss. It will die after 3 hits.
Check the ASM files for customization options. Make sure to specify the sprite number of the fireball in the boss's ASM file!