The Milde enemy from Yoshi's Island. It can be stomped causing the sprite to quickly smush down. The explosion that the sprite causes will function similarly to a cape spin (or Yoshi's Ground Pound ability) to nearby sprites. If the sprite affected is another Milde, they will get stunned and bounce away. All Milde variants stay on ledges, akin to Red Koopas. When a Big Milde is defeated, it will spawn four normal Mildes. These Mildes must be defeated before the Big Milde can be considered defeated -- if Mario allows a single Milde to escape the Big Milde will be able to respawn when Mario returns to the area.
It's a nice sprite, and works for the most part, but there are a few issues that need to be fixed before it can be accepted.
The main issue is Yoshi interaction. When Mario is riding Yoshi and jumps on a Milde (or big Milde when the spinjump define is 0), Yoshi will take damage and clip downwards, usually into the ground. As far as I can tell there isn't any handling for Yoshi interaction, so a check would need to be added in to make sure contact with Yoshi works correctly.
The other issue is that when big Milde is killed by a capespin or ground pound/Yoshi stomp, his top half (flipped) separates from his bottom half by a pixel during one of his animation frames. It's not a big issue since it doesn't affect gameplay, but it looks a bit strange.
While not an issue with the sprite itself, it wasn't mentioned that the big Milde requires the No More Sprite Tile Limits patch, either the standalone or the one included with the SA-1 pack. Otherwise, the Mildes spawned from big Milde have a tendency to flicker or disappear. This seems to be a sprite slot issue since the ones spawned in lower slots don't have this issue - using a modified spawn routine that looks in lower slots could be a possible solution, but I haven't tested this. In any case, using NMSTL is probably the better option (especially considering that the snap/sparkle effects can cause flickering too).
Finally, while not a rejection reason in itself, I would also like to see the .json file improved a bit. While not necessary, adding a graphic icon for the Milde and big Milde would be nice. What's more important though is that the custom list has an entry for both the extra bit clear and set, so both Milde types can be placed from the add sprites window, and that they are named appropriately - for some reason, the custom list entry in this json was named "Ninji".