Deadline

You fire a 1-inch, 60ft beam of senescent energy piercing through creatures, objects, and structures at untraceable speed. An object or structure pierced by the beam has its AC permanently reduced by 4 if it's inorganic. If it's organic, the point pierced by the beam and object or structure's material within 1 ft of the beam decays and ages until it's brittle enough to break by a light touch.

A creature pierced by the beam makes a Constitution save, taking 10d8 necrotic damage on a failure and ageing by 2d4 x 10 years. If this damage would reduce the creature to 0 hit points, it falls unconscious and is stable instead of dying, and it ages an extra year for each point of damage it took in excess of its current hit points. On a success, it takes half damage and isn't aged.

The ageing can be reversed with Greater Restoration or more powerful magic, but only if cast within 24 hours of failing the save. After that time, only a WIsh can reverse the effect.