It's a miracle! Thanks for the advice. Running hot water did not work but soaking it lid down in hot water for 5 minutes or so did the trick.
Prequel:
I first tried to open this particular jar a couple of months ago and gave it a few more tries after that. My buddy with vise-grip-like hands and significant amount of power tried it once too to no avail. He got pretty frustrated, actually. I will tell him I had it opened and see him boiling next time we talk
Today my wife said something along the lines of "So, are we ever going to eat
those mushrooms?". I said I will give another try and if it does not happen, it will go to the garbage. I gave it another good try not long ago and decided to ask here before dumping it. Thanks, Cat!