Dr. Destroy's Sealed Rune of Skill (3-day)
If stored in the inventory, DEX +7 permanently, and has a 5% chance of increasing Critical Rate and Critical Damage by 20% for 10 sec.
Not dropped by monsters.
Cannot be spoiled.
The chances are official (x1). On servers with x10, x100 and higher rates, drop and spoil come more often.