This is pretty cool, but I don't think that it should be reflectable, otherwise you could trigger this yourself while having a mirror shield and deal 20 damage to your opponent. It would require a lot to set up, but you could do something like mirror shield, this card, and unupped pandemonium, and when all your creatures with this are targeted by pandemonium, they deal 20 damage each to the opponent. Hard to pull off, but really funny, and almost guaranteed death if you can manage it. In a duo, you could use explosion/CC + this + mirror/jade shield to deal 20 damage each time.
