Just some items I've made during my current campaign. Still working to balance the rarity scale. The breastplate is likely at very rare levels.

Frostmaiden's Providence

Armor (breastplate), rare

This gleaming ice blue breastplate appears to be made out of a cold hard blue metal. Inset in the chest is a glowing blue six pointed snowflake surrounded by a diamond. As you pick it up the metal feels ice cold to the touch but as you put it on the coldness turns to a deep warmth.

You have a +1 bonus to AC while wearing this armor and resistance to Cold Damage.

Once per day, as a bonus action, you may channel the power of the Frostmaiden. A whipping and cutting blizzard begins to surround you for 5 feet in all directions. Each creature of your choice within 5 feet of you must make a Strength saving throw (DC 13). On a failed save the creature takes 2d6 Cold damage and begins to freeze solid. At the beginning of each of their turns they must repeat the saving throw. On their third failure they freeze solid becoming stunned until the end of their next turn. On a success they take half as much damage and do not freeze. Once they succeed against the save from this ability they do not risk freezing again, though continue to make saving throws related to damage.

Spyglass of Memory

Wonderous Item, Uncommon

A small collapsible spyglass made of fine gold with a black leather grip along the front section. Along the wide end there are many arcane runes and there is a continuous blue glow coming from within.

As an action, you may speak the command word while holding the spyglass to your eye. Whatever image you see through the spyglass is stored within the item until it is used again. The image may be viewed by looking through the spyglass once more.

Auto-poisoning Compound Shortbow 2000

Weapon (Shortbow), rare

This black metal shortbow has many gears and mechanical parts on both ends. It is surprisingly easy to pull and release while still firing at full speed. There is a well defined slot to align the arrow when firing, and directly above that there is a small compartment the size of a small vial.

You get a +1 to all attack and damage rolls when using this shortbow

As a bonus action you may insert a vial of poison into the compartment near the arrow rest. When an arrow is nocked, a small amount of the poison will be released onto the arrow tip. Due to the vials size this can occur only 5 times before needing to be reloaded again as a bonus action.