The thirteenth card, Relinkuriboh, is a Kuriboh that has yet to show up in the anime or manga of Yu-Gi-Oh. If you tribute it you get to draw a card, and it can banish itself from the graveyard to stop one of your monsters from being destroyed by battle. If you want to take advantage of Relinkuribohs first effect you need a way to tribute it, which could be for summoning a higher level monster or to use effects like with Cannon Soldier or Obelisk the Tormentor. Honestly as long as you can get the first effect off it’s probably worth using.