Guppy's Collar is a passive item.

PC RWBY 10FQ (Curse Room adjacent to spawn, in Red Chest)

PC 1CMD B881 (Curse Room adjacent to spawn, surrounded by Spiders)

PC FM7Z 4VAJ (Curse Room adjacent to spawn, surrounded by Spiders)

PS4 FQTL 13FX (Curse Room adjacent to spawn)

Switch XSDE HE2L (First floor Curse Room)

When the Keeper is resurrected by Guppy's Collar, there is a chance it spawns with half a Soul Heart as health. When a health upgrade is obtained, the Keeper will have 1 coin, as well as the half Soul Heart as health. When a second health upgrade is obtained, the Keeper will lose the half Soul Heart and have 2 coins as health.