Gary Gygax once posted that one of his biggest regrets was adding psionics to AD&D. He confessed he didn't know how he allowed himself to be convinced to add them after all.
Why would the man who wrote the rules say he regrets adding them? Because they are an unholy mess, that's why. First of all, in terms of Players, only a rare few get the ability to have them, once they find they do have them, they are a convoluted nightmare to figure out. It took at least one magazine article (actually more than one) to help players grasp a way of conceptualizing the use of psionics without resulting in brain aneurisms.
Now, personally, in my games, psionics just do not exist. Nope, not gonna happen. That means no monsters will ever be written in or otherwise included in my games that have psionics. I don't try to modify certain monsters that have them. I just don't use them. It's that simple for me. I'd rather create whole new non-psionic monster types to replace the monsters of a certain plane which have psionics.
What is psionics really except non-magic magic? I'll leave that stuff for other folks. None of that in my games though. Thank you very much.