The first use of the Mr. Pig meme was during the 2018 reign of Freddy's necessary evil.
It was made I guess as a response to Toots, but didn't go over so well.
It then went dormant from 2019 until sometime in 2020 where it started looking/responding the way it still does today.
The big question is whether or not the moder Mr. Pig anon is the same as the OG.
They've never shown proof when requested.
And, since qresear.ch doesn't store images it's hard to sauce the origin date.
You can search it using Mr Pig or Mr. Pig as a search term and you will see references to it back in '18.