how about Contaminated Ground ? If he can have some land, they will be swamp (Only) and makes him lose 2 life everytime he want to use it. If you can destroy the other land he got, good luck for him to stay in game.

Also, if ou face an opponent with many non-basic lands, Uncontrolled Infestation can be usefull. (Side)

I like the idea of using Urborg, Tomb of Yawgmoth in the deck! The swampwalk mechanic is just perfect here! I would probably add more creature with it, cause they become unblockable. It's fast direct damage that you'll do every turns. Also, the Madness effect is always fun to play!

Great deck!

Thank you for the suggestions! Contaminated ground was something I considered, since I can force my opponent to only have contaminated land, which would be fun. Uncontrolled infestation is nice, but between Spreading Algae doing essentially the same thing and Molten Rain incorporating some burn, I don't know that it's a good fit. That being said, with regards to mechanics-based suggestions, I was considering adding in Plague Beetle or maybe Bog-Strider Ash or something. What should I take out?

instead of Bog-Strider Ash , i would suggest : Warthog (common in Visions), or any 2/2 for 3 mana (Raiding Nightstalker , Krosan Constrictor , Bog Smugglers , Bog Raiders ). The fact is that the Bog-Strider Ash is 4 mana for 2 damages. The other choice still 2 damages, but for 3 mana.

I would take out Basking Rootwalla . Yea, the madness is fun, but you got a 1/1 that can be 3/3 for a certain cost. Nothing else. It can be block easily and don't make a big surprise when it comes into play.

Also, Bloodfire Expert don't seem to synergyse well with the deck. Maybe i'm wrong, but still no evasion, can be boost if you play something in instant (what you don't have). If you still want to play it, i would propose to use Funeral Charm that can make him be swampwalk and give him a +1/+1.

Wild Mongrel is fun when you use madness mechanic. As i said, Basking Rootwalla is not really impressive. If you use Dark Withering or Brain Gorgers , there's many things you can do. You can destroy (or he can choose to sacrifice) a creature. That make him have less presence in the battlefield. Plus, if he don't want to sacrifice, you have a nice creature for 2 mana. Better than the little lizard.

so this is what i would do :

-4x Basking Rootwalla

-3 Bloodfire Expert

-2 Wild Mongrel

+4 Contaminated Ground

+4 Warthog

+1 Mire Boa

OR

-4x Basking Rootwalla

-3 Bloodfire Expert

+3 Brain Gorgers

+2 Wild Mongrel

+2 Plague Beetle or lands. You need lands if you want to play spell that cost you 3-4 at the 3-4 turns

I hope that's helping you :)

I certainly appreciate the suggestions, and will put some heavy consideration into them. The thing is, though, that this isn't really a GRB deck, it's mostly just Gruul. The only access I have to black mana is through Urborg. If an opponent is using any type of nonbasic land destruction, I don't want to have too many black spells or be too invested in swampwalk because it may become useless.

And trust me, the Rootwalla is the cornerstone of this deck and can kick major ass in the Noble format, especially with big creatures not coming out due to mana shortages for my opponent.

The reason for the bloodfire expert is that he boosts when I destroy land, too, including with the Spreading Algae, so if I destroy 2 lands in a turn, he's suddenly a 5/3, which is a big deal with land control.

Still, your suggestions have a great deal of merit and I greatly appreciate the input. You can expect to see a reworked deck in a day or two.