I am looking to create some relics for a story that takes place in the Power Pony universe, so I was wondering if anyone had any idea?

Like just historical relics, or powerful relics that could be stolen and used against the Power Ponies?

Cool

How about
Sombra's artifacts:
Sombra Tomb of spells and alchemic research
Eye of of janus: a necklace that release one inter self
The alicorn gate: time traveling artifact
The Zodiac Keys grup of keys that grants the user a different power base on the constellation

7211872 Both.

I like the concept of a relic that gives unimaginable power but at a price, kinda like the Juggernaut or the newer Cheetah.

Historical relics sound like the perfect place for in-jokes or references to another story.