I think Nintendo's achievement system souls be stamps, but you should have to find them in-game just like you find them in SM3DW for EVERY GAME.
Mario Kart, have to go under water somewhere of to the side into a cave to find a certain stamp...
Pikmin, throw a yellow Pikmin high on top of a leave to grab the stamp...
ZombiU, go through the sewer and kill the something something which is normally or if you're way to get the stamp...
Not just: play multiplayer 50 times.