(You do not use "Polymerization".) Once per turn, when your opponent activates a monster effect (Quick Effect): You can negate the activation, and if you do, destroy it
While supplies last order on time at the release date!
Basically, if youre playing a Commander that has the word Discard or Graveyard in the text box, you should seriously consider the Trademage
While cards with abilities similar to this had existed, the fact that this card was designed to boost your creatures and weaken your foes, as long as they were playing nonblack, was rather novel for the time
Defining these grades is best left to professionals, but you can check out each of them on PSAs Grading Standards page
You just need a shop thats honest about what it sells and run by people who actually care about getting it right