You need all the holy talisman shards to unlock the fleeces in the Crown menu at the Temple in your cult's lands. Here is the full list of their locations:
- The Fisherman in Pilgrim's Passage gives 4 shards: one in exchange for a squid, one in exchange for an octopus, one in exchange for a crab, and one in exchange for a lobster. I recommend using the Ocean's Bounty ritual before going for these as it makes them much more common.
- Sozo in Spore Grotto gives 4 shards: one for 10 mushrooms, one for 20 mushrooms, one for performing the Brainwashing ritual (costs 25 mushrooms), and one for building the Mushroom Sculpture (he provides the blueprint).
- Plimbo in Smuggler's Sanctuary gives 4 in exchange for Eyes of the Witness, which you get by defeating each dungeon's boss after killing the Bishop for that area. I recommend upgrading your weapons and curses before attempting this as the enemies are harder than previously.
- Midas in Midas's Cave gives 4 shards, one per sacrifice made at the golden skull under his throne.
- Death who pops up once per location when you 'Peer into the Darkness' at the teal crescent moon symbol gives 4 shards: one in exchange for a fish, one in exchange for a follower, one in exchange for two followers, and one in exchange for a particular NPC. He is located at the end of the pier in Pilgrim's Passage, to the left of the blueprint shop in Spore Grotto, on the pier at the far right of Smuggler's Sanctuary, and at the top right of Midas's Cave. He only shows up at night and you will need a large fish to complete his first quest.
Once you unlock the last fleece (be sure to re-equip the one you want to use), you'll earn the achievement. Please let me know if you have any questions or comments!