A set of Pentimoes consists of 156 tiles. They include 4 Ouroboros, 2 of each of the 3 Quints, and one each of every remaining unique sequence of numbered pips.
The Ouroboros are wild / trump tiles. They may be played from the hand, and score points based on the value of interacting tile-faces; and can make any valid steals, scoring those points as well. Tiles may not be played on, or steal an Ouroboros. Playing an Ouroboros obligates the player to an additional move (after drawing an additional tile from the stock). They have no negative value in final tally.