To add to that you also have to have the second player present when you lay the last hit on the final boss. Just have to hit start on them to steal one of your lives and then kill him if you're all by yourself.
Finished off Baseball Stars II this morning so here is a pic from both one and two.
After that I started working on Advanced Dungeons & Dragons: Hillsfar which was the last of the 4 AD&D games I needed to finish for my personal list. It also marked a massive milestone for my personal list as it was the 500th licensed NES game I've beaten from start to finish, all on original hardware with no cheats! Very proud of that accomplishment!