Are we sure Mars is Mars? What if it's a trick, and this Mars is actually part of her Throne World illusion?
It's just extremely hyper realistic, just with one new addition with the Relic.
Or maybe, her actual throne world is the Altar of Reflection with Mars & her "Throne World" being just a memory?
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No. Mars is Mars. You can see the Witness get mad about Mars being returned during the final cutscene of the Witch Queen.