Favorite Card to use (Past or Present)

During this past week while I was trying to put the finishing touches on my deck for FNM, I found myself reflecting on all the cards from the past that i had played with and have own. I asked myself if I had to choose 1 card that I have found great joy in using against my opponents what would it be?

After sitting around and thinking it over, I think I would have to choose Polymorphist's Jest from M15.

I mean think about it.. Just as your opponent is going to make this big swing you play Polymorphist's Jest for only 2 blue and 1 colorless and then you turn all of his/her huge creatures into 1/1 blue frogs, then to top it off all of those creatures loose the abilities. How PIMP is that? then if you happen to have out Circle of flames. just one massive board wipe for them.

I don't know if its just me but I think that's so funny especially if you are playing against a hyper aggressive player. So now that you know mine whats yours?