My opponent cast an Ethereal Armor on a Silent Hallcreeper that either already had 2 +1/+1 counters on it, triggered the ability to gain them when it attacked that turn, with an Unable to scream and either 1 or 2 doors already in play. That should have given it +3/+3 or +4/+4, but instead gave +6/+6 because it was a 9/9 that returned to a 3/3 after I destroyed the Ethereal Armor.