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Original Description:

But the Tree of Harmony isnt going to let her go that easily, even if it means the Tree needs to take control of her body itself.

This form is something that only occurs for brief moments in the PortalSparkle AU’s take on Twilight’s Kingdom - While the Mane 6 recieve their Rainbow Powers, you can’t exactly easily heal somepony who isn’t alive, so the Tree of Harmony possesses Portal Bump’s body, leading to the Portal of Harmony. This continues into Portal Bump’s immediate rise to Alicorn status once she tears through reality after being made to open the portal to Tartarus, being revived when she lands in the Ascension Realm.