I was playing guacamelee the other day and I noticed that they have obvious references to some metroid elements such as chozo statues and metroids themselves. I found it a little weird since the game is for playstation and metroid is Nintendos IP, they even went as far as actually calling their chozo statues "chozo statues", so I found it hard to believe that nintendo would of actually OK-ed it which leads me to question if they even needed permission in the game?
Not only that but what would be the legality of say Saints Row 4 having in their commercial something along the lines of "If you like grand theft auto, you'll love this!!!" or someone making a DR Mario inspired game and promoting it online using a title along the lines of "I made this 3D DR Mario inspired game"
What would be the legality behind mentioning another IP in reference to yours?