If you can ignore the restriction, then you've paid a cost for free and get to reap the benefits of more power for less mana
This can be a nice tempo card that you can use to close out your opponent, and thats especially true in Blue/White, which can get some extra value from the tapping
Now we've got Final Parting, which is literally merging Diabolic Tutor and Entomb together into one card, even including the combined mana cost
cards on your field is equal to or less than the number on your opponent's field, set up to 1 of your [Foxy] cards as active
As was mentioned, Ash Barrens is not a bad land card, but if you intend to speed up the rhythm of the Limit Break deck, youll need lands that effectively drop in and provide colored mana or have special effects that synergize with the rest of the cards