I searched on the internet but I didn't find the meaning of "メチメタ" in the below sentence: いにしえの書物には魂が メチメタこもってっからひとを呼び寄せたり乗り移ったりすっかんね。
Judging from the live Tweet search, this seems to be an adverb meaning "very" or "a lot". I didn't know it, either, but it's intuitively understandable as a mix of めちゃめちゃ and めためた. This word seems to exist, but there is no need to memorize it. It is used less than once a week in the entire Twitter community.