Concave Stone

Once per night, a boon choice has a 25% chance to grant one additional random option from the same offering.

Use it when

Use it after the main Boon slots are safe to fill with an unpredictable extra boon.

Limit

The extra boon is random and can occupy a main Boon slots the build intended to reserve.

If it is absent

Use a god keepsake while the build still needs a specific opening boon.

When to replace it

Keep it while its condition supports the current route, then replace it when another keepsake solves a more immediate constraint.