I'd consider Dragon Quest : Rocket Slime a hidden gem since I don't hear many people talking about it and most people just stick with the dragon quest rpgs. Rocket Slime is one of my favorite DS games too.
It is part of the game and I think in some part of the game, Omega-Xis says that when you put your visualizer you can't see humans and to be careful. =0
It's been a while since I've played since I have done almost everything in the game. Maybe about every month unless I'm in the mood for playing the game.