Phineas's Robe and Slippers were spoils of war won by Percy.
The Heroes of Olympus[]
The Son of Neptune[]
When Percy, Frank and Hazel come to Portland, Oregon, they encounter the blind seer Phineas.
Phineas was one of the souls Gaea revived. In order to get information from him as towards the whereabouts of Alcyones location (without having to hand over Ella the harpy), Percy challenged Phineas to a fatal game of chance drinking Gorgons Blood (another spoil of war). Since drinking the blood from the correct side of a Gorgon can heal while the other can kill Phineas agreed because of the prospect of being able to see and see the future. If Percy won, he would get a pre-written slip of paper telling Alcyones' base. Percy ended up being the victor thanks to Gaea falsely influencing Phineas' decision (viewing Percy's life as more important). Phineas disintegrated leaving nothing behind but his robe, bunny slippers and the piece of paper telling the location of Alcyones. Frank described them as the most disguisting spoils of war, so much so that the trio did not even bring them with them.