Ring of Instant Armor (3.5e Equipment)
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Idea inspired by works from Will Howell Ring of Instant Armor: This steel ring has the image of a suit of armor engraved upon it. Whenever you are in a dangerous situation (e.g. hit in combat, attacked, etc.) this ring flashes and transforms into a suit of +1 Full plate. This lasts until the dangerous situation is over (e.g. combat is over, attacker is dead, etc.) or by casting dispel magic upon the ring. If you are wearing other armor and still wearing the ring, the ring will still conjure armor and you will be crushed. You take 1d6 damage if wearing light armor, 3d6 for medium and 5d6 for heavy armor.
Also, the original creator did not realize that when he said any dangerous situation, if the wearer fell in water and started to drown that the ring would conjure the armor. If you are drowning or in rapids, being attacked while swimming, etc. the ring will still conjure the armor.
Moderate (DC 19) Conjuration;CL 6th; Forge Ring, Craft Magic Arms and Armor, Telekinesis; Cost 2,500gp, 200 XP, 5 Days; Activation: See Text; Weight: — and 50 lb.; Market Price: 5,000 gp