Due to her harrowing experiences within the Maze, the sin that Robin was forced to pick - Gluttony - has gained sentience within her, and seeks to corrupt Robin and everyone around her with its influence.
At present, Robin has given no ground to the spirit, but that's mostly because she secluded herself in an environment where the spirit couldn't thrive. As it currently stands, the Sin Spirit simply induces a supernatural ravening hunger within Robin as a constant effect, and all who come within five feet of her if they fail a DC 25 Will Save. The hunger lasts for 1d4 minutes after Robin leaves their presence. This hunger has no effects on its own, and does not magically compel people to eat. However, if they do give in, the hunger instead stays for the rest of the day. If they consume food beyond what is necessary during this day, they must succeed on a DC 25 Will save. On a success, they continue to glut themselves only for the rest of the day and show minor signs of visible corruption, they gain a few pounds, but that's it. On a failure, the hunger stays until the end of the week, the character feasts every opportunity they have, and over the course of the week the character in question will gain enough weight for it to be noticeable to all. Robin directly touching a character both immediately leads to the third stage and increases the save DC by 5. The curse stacks up to three instances. The first instance has no effect, the second instance offers a -1 penalty to Strength and Dexterity, and the third instance offers a -2 penalty to Strength and Dexterity and a 10 ft. reduction in movement speed.
The effects of the Sin Spirit are accelerated and enhanced on Robin, however. Every time she is presented with food, Robin must succeed on a DC 20 Will save or consume it in its entirety, or take 1 point of nonlethal damage from hunger pangs. Until the spirit is satisfied with its progress on corrupting her, this will not satiate her hunger but instead worsen it. Any healthy or sparse foods will be noticeably replaced with more tempting and sweet versions.
Once the spirit has corrupted Robin enough, or two other people have failed their saving throws due to its effects, its power and influence will increase.