Back in June, for instance, youd have to spend at least $1,100 per box, which was already obscene
Dusk // Dawn is tailor-made for this deck since you wont lose any creatures (aside from your commander), and ditto for Slaughter the Strong
Bouncing a damaged Kronk or The Prince, Never Gives Up can be a great way to heal them so they can be played again, while bouncing a shifted Hercules or Cinderella will always give you two cards back, and even allow you to add one of them to your inkwell if you're in a position to play the Floodborn card for full price
Mystic Remora (T1, Ext) The first card on this list heralds from good old Type 1
Clan Defiance It may not look sexy, but Clan Defiance is the best X damage spell in Gruul, and better than most Red options with its ability to shoot down two creatures as well as Blaze an opponent