A card will be downgraded from NM to Ex if it has any of the following

• soft or dinged corners of any significance
• noticably off-colored or fuzzy printing
• even minor creases, scuffing, fading
• miscut so there is no white on one side of the border
• even minor gum or wax or other stains or spots

Of course a combination of all these defects would grade the card even lower, grading can be very subjective, so always better to grade conservatively. To be more specific people use grades of Ex+, and Ex- in addition to Ex. But if it has any tears, writing, loose borders, non-minor creasing, soiling, discoloration, spotting, staining, etc, then the card is not Ex, it is VG at best. If the card is slightly better than Ex+ then it is usually called NM-. It really has to be close to perfect to be called NM.
Wacky Packs, grade your wacky packages.