PG, the evil/insane stuff is basically slander and you need to retract.
Even aside from that, the litmus test for the mental wherewithal to consecrate validly is simply that he knows what he's doing and is capable of intending to do what the Church does. He basically would have to be so far gone that he didn't know who he was or what he was doing. Lack of prudence or sound judgment or eccentricity etc. do NOT render someone incapable of validly consecrating.
I personally know someone who was at dinner with Bishop Thuc AFTER the consecrations of Bishop Guerard des Laurier and Bishop Zamora and Carmona. Bishop Thuc was at the table with priests who spoke several different language and he was actually switching from one language to another and keeping track of each thread of conversation. That is NOT a man who could not validly consecrate.
You could easily make the same case for Bishop Mendez, but I won't go into his personal issues. What's interesting is that Bishop Mendez had a stroke not too long before consecrating Bishop Kelly, and one relative testified that Bishop Mendez didn't recognize him (or her, I can't remember) just days before the Bishop Kelly consecration. When Bishop Mendez was ordaining Fathers Greenwell and Baumberger, Father Kelly had to ask him to repeat the essential words of ordination several times because he badly slurred the words. In fact, one of the priests has said that Bishop Mendez pronounced everything correctly and then inexplicably sped up and slurred only the words of the essential form. Bishop signed the letter of ordination with an alias name and then, when confronted about it by Father Peter Scott of the SSPX, he denied in writing that he had ordained Fathers Greenwell and Baumberger.
So, ironically, Bishop Kelly's arguments against Bishop Thuc can be turned right back on him.