Help me choose the right rat....

[kal4444]

I'm making a Marrow-Gnawer rat deck.  I'm going to have a Thrumming stone in there as well.  I have 2 choices either Rat Colony or Relentless Rats. 

I'm personally leaning towards Rat Colony due to its 1 less cost.  What are your thoughts???  Thanks

[Elan Morin Tedronai]

https://deckstats.net/decks/196358/2482216-rats
That's the deck you're making, I assume? Well, you're better with Rat Colony for sure, however you can try them both actually. Put equal size? Or just 5 or 6. You can balance them, perhaps? They're the only Rats that can be any number of cards. It's an EDH deck and it should be in the Commander Deck Reviews. I was wondering about making a Rat deck not EDH, but Modern. Maybe next year.

[Landale]

The cost difference is almost negligible. The bigger concern is durability vs synergy here.
Rat Colony grows even with Marrow-Gnawer's tokens but gets wiped out by any cheap 1 damage to each type effect, Blazing Volley, Marrow Shards, Sandstorm, Dry Spell, etc., if you're not including ways to increase toughness Ascendant Evincar and Death Pit Offering are the ones that immediately come to mind for mono-Black. Even if your group doesn't normally run these types of spells, if the deck becomes a frequent thing they may choose to add some in if you can't reliably bulk the rats up.
Relentless Rats has a cap on how large they can make themselves due to only caring about Relentless Rats, barring something like Helm of the Host being in the deck, but they're going to require actual board wipes to get rid of.

Personally, I think I'd go with the Relentless Rats outside of possible budget concerns since they run almost an extra dollar each.

[stuffnsuch]

Relentless Rats is way more fun after playing a Mutilate as a one sided board wipe.  Soul Foundry is also your best friend when you need actual copies of a specific card.