It’s difficult to place the exact origins of Operation Delibird, the tradition that sees Pokémon players send out rare and exclusive monsters every Christmas. Gamespot messageboards mention it by name, but the idea was formed after the release of Pokémon X and Y in 2013, due to the addition of the Wonder Trade feature (renamed as Surprise Trade in the most recent games), which lets you send your Pokémon to a stranger with no idea of what you’ll get in return.
Players use this feature to send out hundreds of rare Pokémon on Christmas Day and Boxing Day every year, to hopefully connect with children who received the game for Christmas and add something special to their first playthrough.
Operation Delibird was named after Operation Zubat – an attempt to flood the new Wonder Trade system with annoyingly common Zubats – and Delibird, a Father Christmas-cosplaying bird Pokémon with the signature move “Present”. But, instead of annoying the recipient of your Pokémon, the intention is to trade something much more desirable as a Christmas gift.
Source: Eurogamer Meet the Pokémon fans who send hundreds of rare monsters to kids on Christmas Day