That would be Visual Boy Advanced using a complete bestiary. Pretty simple actually, for all of the enemies in the game. Just organizing them that takes some time.
Speaking of, would you like me to separate the sprites that are new to DoS into individual images, give a big sheet that's just a sprawl of all the monsters, or just give them to you as I had planned to upload them (all of the sprites and their recolours in the same image)?
Edit: Well, here's how I planned to do it. I can reorganize if necessary, but if not:
LINK
Terribly sorry about the lack of transparency, but the only program that would allow me to do it in a reasonable amount of time wasn't working.