Planet X is probably the weakest all of conspiracy theories. Not necessarily the craziest even, but certainly the one that holds the least water. There's just no basis for it except countless "channelings" and one article written in 1983 that was later easily explained (the mystery objects were distant galaxies).

It's a very intriguing IDEA, but it doesn't hold up. I guess it never goes away because the idea of that much doom with that much SCOPE is so alluring to us woo woos.