It is a bit tricky to find though since it is on a side street, basically when you are walking down one of the arcade streets and you get to about here (the Ameyokocho building, which is also definitely worth checking out):
You turn onto a side street and blammo, you are right there:
I give the shop a score of minus 1000 in terms of its external appeal. Whereas pretty much everywhere in Osu is vibrant and colorful, Mandarake is located in the only bit of grey dreariness in the neighborhood, surrounded by ugly parking lots. And the building itself is an ugly grey blob. But once you get inside its a different story.
In terms of stuff they have about the same type of selection as the Fukuoka Mandarake that I have featured on here numerous times. The first floor is video games and comics, while the upper floors are toys and cosplay stuff.
Their Famicom selection isn`t as good as that in the Fukuoka Mandarake (which is surprising given that Nagoya is more than double the size of Fukuoka). They keep all the loose carts in this basket here. The prices are probably the best you will find in Osu, though that isn`t necessarily saying much. They are fair and you might find the odd bargain in there.