This is a comprehensive list of all Accessories in the game, by default sorted by requirement. Accessories are primarily based on Mysticality as requirement and give a wide variety of effects. Since there are three accessory slots, some can only be equipped once. At present, there are no means to increase the number of slots, even though the items are "applied" to various body parts.
A number of accessories must be worn singly, i.e., you cannot wear more than one at the same time. A list can be accessed here.