How do you know it's 12? If you're going by pictures, i could have told you that. However:
1) There are teeth in the back of his jaw invisible because they are in his mouth. 2) The nemesis is constantly changing appearance with each attack. 3) the nemesis in the game and in the movie are different slightly, including the shape of the mouth and teeth, and number of teeth.
Tiger Spider. Has several different names compared to where you look, and which version of the game you mean. Found after running from the bolder in the sewer system after Enrico Martini is shot by an unseen foe. The Spider not only grabs you, shoots poison at you and bites you, but there are also smaller spiders that burst from it's body after death.
As for polygon count, well i never claimed to know anything about the tech behind the games, on what the games include such as story, timeline, connections, facts etc. I do know that it is insanely high, but i don't even know what is high for polygons in Mario 1. Stick to the game, not techy stuff behind the game.