Seems like a really powerful card. Of course, in an tight engine, the on-play benefit of this card will be amazing. At $4, they can be fairly easy to gain lots of them. And they chain in a pretty amazing way, too.
The on-buy effect is also pretty powerful. Play a Chancellor and then use the on-buy effect to put KC-KC-BR-BR-BR (or whatever dominant combo is in the board) on the top of your deck. Now, you might have have $9 to spend that often (to put 5 cards back), but there are lots of two card combos or self-combos (Treasure Map, for example).