This will appear to be a beautiful but naturalistic quarter staff of full size. It will radiate magic. This is a +2 weapon, adding to both Hit and Damage to the staff's normal 1d6.
The first time this staff is used in actual combat, long cruel thorns will grow out of it, doing 1d3 +2 HP of damage to whomever is holding it, with no roll To Hit required. The wielder must drop the staff immediately, or take automatic damage again next round.
Should the wielder choose to endure the damage (or is somehow immune to it), any creature struck by the thorn staff will now take 1d10+2 HP of damage. The thorns will disappear when the staff is dropped.
Optional: The thorns may be poisonous, requiring the victim to roll a Save vs. Poison, or begin taking 1 HP of damage per minute until cured or dead.
Image: Armor by Erda Estremera, released under the Unsplash License, modified by Seth Kenlon