The Ultimate Mirror!!!
$5 in Eth Giveaway, check the video description!
The first time I played against a guy that whipped out archimedes mirror... i was so confident i was gonna win, until i got completely away by surprise when it managed to wipe my entire board of creatures. This is a very powerful card that, if played well, can essentially give you 2 board clears for the low cost of one at 6 mana.