Lore wise, what are the most powerful objects/artifacts in League Of Legends and why

From just a Runterran perspective, the World Runes. Picture nukes that you can hold in your hand (read Ryze's short story to get a better picture). Now, overall? I think it would likely be the crown Pantheon (not the current literal one, the aspect) used to ensnare Aurelion Sol, but the World Runes probably still right behind it.

Runner ups would be Illaoi's idol, Ashe's True Ice bow, Jayce's Mercury Hammer core, Yorick's water pendant, and I'd say the entirety of Galio

The World Runes.

The most powerful that we might have seen might be the cosmic egg seen in the bard video. I mean Bard doesn't seem to have a problem with the world runes lying around in the reach of mortals,but when the cosmic egg got into the hands of the old man(and accidently cut off the tip of a mountain),he instantly traveled to the place to take the egg away.

• World Runes, obviously. Magical nukes are essentially what they are.
• Hextech is an emerging technology. It's designed to allow non-magical folk to essentially wield magic through relics. Cheap, synthetic hextech gems are good but not as good as the real stuff: Brackern crystals from the Shuriman desert. This stuff powers Jayce's Hammer/Cannon, as well as Ekko's Zero Drive. Also... Jhin has proven that the effect of combining hextech with innate magical power is DEVASTATING and extremely powerful.
• Darkin weapons are artifacts of doom, naturally.
• The Shadow Box that corrupted Zed seems more than just a description of a forbidden technique, but we don't know much about it.
• True Ice, and weapons made of it. That stuff will never melt (exceptions exist, like Ornn's heat), and can be used to freeze others.
• Bard's chimes and moonstones are general relics that are neat, but we're not quite sure what they're capable of. Moonstones can possibly repel the Void, and as for chimes... who knows?
• The Sun Disc in Shurima is responsible for turning people into Ascended, if they are worthy. Truly a powerful artifact, especially now that it's been restored.
• The dagger that made Elise immortal.
• Mordekaiser's skull. It can instantly resurrect him, provided foul magics are used (like those of the Shadow Isles).
• Finally, the key that Zoe now has... Fiddlesticks's old key... we probably don't want to know what it opens...

If I missed anything, please add to the list.