That's likely a fairer cost for Bubbling Muck than a single . The "Destroy target Swamp" line is rather odd though. Upping the cost from 1 to 4 (and from common to rare) is probably enough bump to restrict the combo potential, so this is really only any good if the opponent has Swamps... but it's a pretty weird kind of sideboard card. (Cf Cryoclasm.)