A clue token is a token artifact that allows you to pay two generic mana, tap it, and sacrifice it to draw a card
There's a promo card variant with the Magic logo stamp, for instance, which has understandably remained cheap
These will transform after you fulfill some kind of condition on the card, usually either an activated ability (i.e., paying to exile Terra, Magical Adept) or triggered ability (i.e., having six permanents in the yard for Exdeath, Void Warlock at end of turn)
What's going on here
First up is Marina Vendrells Grimoire , a blue-mana-powered artifact with some interesting new mechanics
During the era of the Weatherlight Saga we have winning cards such as Mirri's Guile or Hanna's Custody or Orim's Thunder