This pendant is made with iridescent gemstones and swirling fluid-like designs. 

Illusory Transformation. While wearing this amulet, you can use an action to transform into any creature or object you have seen within the last 10 days that is up to two size categories larger than you (from Medium to Huge, for instance). You gain the creature's appearance, size, and Creature type, but you retain your alignment, personality, abilities, and statistics. If you transform into a creature, you also gain access to that creature's movement speed and senses.

A creature can discern that you are transformed by using it's action to inspect your appearance, and succeed on a DC 17 Intelligence (Investigation) check. The transformation otherwise lasts for 24 hours, though you can use your action to end the effect early. Once you use this amulet in this way, you cannot do so again until you finish a long rest.

Notes: Shapechanging, transmutation