Thorns is a status effect which causes the enemy to take damage every time they attack a Thorned user. The damage dealt is equal to the value of Thorns. The status effect lasts until the Thorns user's next turn begins.
Interestingly enough, if the user has Thorns and then puts out burned dice, they will take extra damage from their own thorns.
If the enemy attacks a player who has Thorns, causing both of them to run out of health, the player will survive and win the fight.
In the Parallel Universe episodes, Thorns is changed to Thorns?. This status effect instead heals 1 health per each thorn per each attack from the Thorns? user. This status lasts until the Thorns? user's turn ends.
The gadget Needle grants 1 thorns to its user.
The Rose Shield status adds thorns each time the user takes damage while it's active.