Why is Marshadow in the OU tier?

Question

Marshadow is supposed to be an unreleased Pokémon, but when I typed "Marshadow" in Showdown, it didn't say ''Unreleased" but it said OU. Is there a Marshadow event that I don't know about?

Comments

The Marshadow event has already started. However, I don't know much else about it.

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I believe there is an upcoming Japanese Marshadow event to promote the new movie

Answer 1

Many people Hack in the Pokémon community to get Pokémon they want. Some of these Pokémon are unreleased event Pokémon including marshadow. Also the event has started in Japan for the release of the new movie.

Comments

A Pokemon is allowed in OU only when it's obtainable without hacking.

Answer 2

Marshadow is currently not allowed in OU and will likely remain that way for a long time.
source

Comments

Thought I'd also quickly throw in why it was in OU at all: its distribution began in Japan a few days ago, and Smogon sends anything new to OU to gauge where it may belong tier-wise. Marshadow ended up quick-banned which is why it's no longer allowed.