Gungnir

Gungnir, Old Norse for "swaying one", is best known as the personal weapon of Odin.

History
Made from Uru by the Dwarves of Nidavellir for Bor, Odin's father for his war against the Dark Elves, his son Odin subsequently used it in the conquest of the Nine Realms, and then to subdue his ambitious daughter, Hela.

Now the undisputed King of Asgard and Allfather of the Nine Realms, Odin- and Gungnir itself, was seen as a symbol of Asgardian might and prestige.

Description
Gungnir in myth was said to be able to hit its target, no matter the strength or skill of the wielder. In addition, the Marvel comics add the same enchantment on Gungnir that Mjolnir possesses, allowing it to return to its wielder's hand.

Passive Abilities
God-Killer: This weapon ignores all immunities and resistances to physical and a single type of damage (Radiant)

Magic Conduit: Magic may be cast through the artifact instead of a normal focus.

Resistance: This item gives you resistance to a single damage type (Radiant).

Power Immune: The artifact is immune to all effects and powers not cast by the wielder. This doesn't extend immunity to the wielder. It cannot be broken, transported (seperately from the wielder), or altered by an opponent.

Unmissable: You have +3 Attack Bonus and Damage Rolls while wielding Gungnir. If your Wisdom modifier is higher than 3, you may use that instead of +3. Should the attack miss, the target will take 1d8 + 3 Force Damage and be staggered.

Fortify Health: You gain 30 base health while wielding this weapon.

Bifrost Bridge Key: This item may be used to open and focus the Bifrost Gate on Asgard.

Active Abilities
Return: This item may be returned to the user who threw or dropped the weapon last as a bonus action from any location in any plane by the most direct path. The weapon will return to the user's hand by the user's next turn if not on the same plane. The DM may rule for damage to be taken as part of its return, for example if a creature is between the spear and the wielder.

Call Bifrost: This item may, if conditions are right, allow one to summon the Bifrost to return one to Asgard or to teleport someone to any location. The user must concentrate for at least 30 seconds. A three foot wide cylinder centered on the caster will appear and teleport to a location, specific or not. Any being or object not within this cylinder completely (one part in, one part out) will suffer Necrotic damage equal to (body percentage out of the area x 10, from 1) x d6 that ignores resistances and immunities. The part will travel in the Bifrost alongside all else within this three-foot wide cylinder. You can only do this four times per day.

Cast Out: This item summons a beam of Bifrost energy that blasts a target for 5d10 Force damage and sends them through to another random location. You can only do this once per day.

Restore Slots: You regain all missing spell slots as an action. You may only do this once until completing a long rest.