Silver skulls, the skull door and the Petrified Garden ritual

There are 69 Strange Silver Etched Skulls, handed in at a skull door beneath the Petrified Garden. Rewards arrive at 10, 20, 30, 40, 50 and 69 skulls, and handing in all 69 unlocks The Call From Beyond and the ritual needed for Ending 4. The game shows no hand-in counter, so keep your own tally.

Rewards

Skulls handed in	Reward
10	Ancient Stone Duck Figurine, which adds collectible-marking charms to Umbada’s shop
20	Fossilized Fish accessory
30	Flying Mushroom Fossil accessory, a short upward float
40	Fossilized Anemone accessory
50	Sonic Crystal Fossil accessory
69	Ritual access and the Pigeon Fossil

Fossil effects that have been measured are on the accessory list. One player says 67 skulls were enough; every guide gives 69, and the achievement needs all of them.

Reaching the skull door

The door is under the Petrified Garden, which you enter by jumping off a Wing Altar during its teleport animation. Reaching the door needs all four lenses in the Mask of Second Sight and all five Trident Keys, placed in the colour-matched statues of the garden.

Where skulls hide

Skulls are spread across every region, often on ledges above normal routes. Reported spots include the Siraatsu Castle roof, the Ancient World cliffs, the ledge above the fifth Wind Gem and a hidden island behind a shed on the Deimpo Mausoleum roof. Many need the Cestus uppercut as an extra jump, or all five Wind Dashes, so collect the late skulls after the fifth Wind Gem.

The Petrified Garden ritual

Waking the garden unlocks Living Stone (13.6% of players). With all four lenses and the five Trident Keys in place, the ritual continues in this order: wake the fountain, strike the glowing fish statues, activate the symbols, then jump into the house. Patch 1.01.04 added settings that make some late-game puzzles less punishing. Handing in all 69 skulls completes The Call From Beyond (3.1%).