One solid stax effect you could consider is Contamination if you want to go that direction. With Meren, you can always get the creature to sacrifice to it, so against non-black decks it makes all of your opponent's mana effectively colorless (still have to deal with their mana rocks), but lets you still play pretty easily. Another card that I can't recommend highly enough is Bane of Progress. In my deck this guy is constantly being tutored for, especially against artifact based combo lik e Sharuum (although it can do serious damage regardless). I'm not entirely sure why you run Noose Constrictor (no offense) other than to maybe get something in the graveyard to pull back out with Meren. If that is the case, I definitely recommend Fauna Shaman over it, which can help you get your answers while allowing you to discard the creatures you'd like to reanimate.

WhisperingBlade

Fauna Shaman and Contamination are both very much on my radar for cards I am looking to acquire. But I am in many respects on a budget with this deck, and Noose Constrictor fills out my 2-drop slot and works reasonably well. The meta at my store consists almost entirely of burn and aggro decks so you need a very tight curve to get blockers in the way, to the point where Wall of Blossoms is arguably my best two-drop in a lot of match-ups. I'll have to consider Bane of Progress, but I think you are coming at this from a multiplayer commander perspective. Mana rocks really aren't as important in duel commander as they are in multiplayer, and at any rate I would under no circumstances resolve a Bane of Progress if I had certain artifacts in play like Ashnod's Altar or Birthing Pod.

That's fair, I do typically play multiplayer more often than I play duel commander, so maybe I'd get more use out of Bane of Progress. If you are having trouble with aggro, I'm starting to see why Skinrender might make more sense. You could always try Noxious Gearhulk, Duplicant, Wurmcoil Engine, or Demon of Dark Schemes to have some better late game answers against aggressive strategies. I've also found that Khalni Garden can be helpful for producing another creature to sacrifice or to chump with, but your mana curve looks excellent and I would be careful messing around with that. Ishkanah, Grafwidow can be very helpful in fighting aggro and voltron, especially voltron commanders with flying like Sigarda, Host of Herons and Dragonlord Ojutai.

WhisperingBlade

Skinrender is targeted removal on a 3/3 a creature that I can get back, and it totally hoses Skullbriar, the Walking Grave which is one of the most consistently dominant decks in the local meta. I have considered all of the six-drops you have mentioned at one point or another, and of the group the only one I would likely include is Wurmcoil Engine, if I decided I wanted a second six-drop. Demon of Dark Schemes is basically a worse Massacre Wurm and I can usually tutor for the worm when I need it. I should probably give Duplicant a second thought though. Noxious Gearhulk is a solid "will test when it rotates and comes down in price." Khalni Garden certainly fits with the overall strategy of grinding out value in the mid-late game, but will require testing. I probably have too many tap lands in the deck as it stands right now.

Ishkanah, Grafwidow is an interesting case especially in a meta with some serious flying threats like Jenara, Asura of War and Brago, King Eternal. Along with Grim Flayer it doesn't make the cut because this deck is remarkably weak on delirium, and not for lack of self-mill. I only have one artifact creature, two enchantments and zero planeswalkers (flip lili isn't a walker in the graveyard). It turns out that a deck that wants to have as many as 40 creatures (if you look at lists on mtgtop8) doesn't tend to get delirium very early. Though it usually gets delirium eventually, which is why I still include Traverse the Ulvenwald to tutor up late games threats.

I've noticed that in my games that I usually get delirium turn 3-4, although I've opted to run 4 off-color fetches. Understandable though, I play more multiplayer than duel commander, and more casually than what you might be seeing at your LGS. Out of curiosity, what do you think of Treasure Keeper? It seems like an absolute gem in Meren to me, getting some card advantage (and potentially more graveyard reanimation targets later down the road) while being a fun, random effect.

WhisperingBlade

I need more fetches for sure, but there are a large number of things that need to be improved so I try to go for the most bang for my buck when making improvements and fetches are expensive and hard to come by at my LGS. I have actually never ordered cards from a singles seller since I started working on this deck last summer.

Getting delerium on turn 3-4 isn't always going to be fast enough. Against the all-in aggro decklists you are looking to stabilize or lose around turn 4. But again that's a difference between 1v1, 20 life commander in a meta dedicated to playing that kind of game and multiplayer EDH.

Treasure Keeper is likely going to be excellent for multiplayer, but in duel commander it is harder to say. It is still a 3/3 for 4 that doesn't do anything the turn it enters the battlefield. If it put revealed cards into your graveyard it might be a different story. The biggest news for Meren EDH players from AER, in my opinion, is Walking Ballista, which is just a more aggressively-costed Triskelion for the mike and trike combo. You can even reanimate it with Meren if you have no experience counters and it will die right away for an experience counter and other triggers. If you have Mikaeus, the Unhallowed in play it gets reanimated right when it dies and you just combo out. The most interesting card for golgari players in general is the Winding Constrictor. Keep an eye on Yahenni, Undying Partisan too, it is a great sac outlet for 3 mana and is a very aggressive card overall. Could be a great mono-black aggro commander/tiny leader too, if that interests you.

Okay, thanks for your thoughts!