Tier 5 Raid - Shiny Darkrai .

Darkrai had its first debut in Tier 5 raids globally during the Halloween 2019 event. It however, would not be available shiny until the first Team GO Rocket Takeover event.

Even if you caught one earlier, the Darkrai could not be transferred to the main series games until the HOME v2.0.0 update, which supports Brilliant Diamond & Shining Pearl and Legends Arceus.

For this file to be transferable across games without any stats oddities, you cannot modify any immutable values.
Read here: Relevance of HOME tracker