Amulet of Stykur

While wearing this amulet, if your alignment is good, then your Constitution score is increased by 5, to a max Constitution score of 20.  And your Strength score increases by 2, to a max Strength score of 20.

You can use this magical amulet once a day to trigger its effect: Shield spell.

An invisible barrier of magical force appears and protects you. Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack, and you take no damage from Magic Missile.

If your alignment is neutral, you gain no benefits.

If your alignment is evil, then, while wearing this amulet, your Constitution score is decreased by 5, to a minimum Constitution score of 5.  And your Strength score decreases by 2, to a minimum Strength score of 10.

You can use this magical amulet once a day to trigger its effect: Shield spell.  However, roll a d100 to see if the Shield spell works.  Anything from 1-10% will allow the spell to work as intended.

Notes: Set: Constitution Score, Must attune to item at a short rest, Buff, Jewelry