What do you think Abzkaban? SynergyBuild? hkhssweiss? It'd be great to hear your thoughts on this.

Heya goldlion, I personally love the idea. My friend uses Carnival of Souls in his tuned Teysa, Orzhov Scion deck and it's pretty degenerate.

In regards for tuning for competitive play, if going all out the fast efficient mana rocks. The standard usual Mana Crypt , Mox Diamond , Chrome Mox , Sol Ring , Mana Vault should be included. All tutors for consistency ex. Vampiric Tutor , Demonic Tutor , Diabolic Intent , Imperial Seal , Grim Tutor , Enlightened Tutor , Worldly Tutor , and I would also include Idyllic Tutor .

Next would be your main avenue for balancing your combo pieces. You need the life gain, so running all your soul sister effects are priority. I would run pretty much only the one drop ex. Soul Warden , Essence Warden , Soul's Attendant , and Deathgreeter . Both Blood Artist and Zulaport Cutthroat doubles as your win cons when you have every thing set up. You also need to set up ways to proc Ghave when your Carnival is on the field so in goes Ivy Lane Denizen , Elenda, the Dusk Rose , Juniper Order Ranger , and Champion of Lambholt . All of these ones can lead to infinite triggers and than infinite tokens.

Card draw is fairly important, so the usual engines are in ex. Sylvan Library and Necropotence . With having non-token creatures dying, you have them listed but they will also go in, ex. Midnight Reaper and Dark Prophecy . Dark Confidant will also go in with the low CMC curve. Skullclamp will also be an outlet for you as well to draw out your whole deck. You can test it out but Mentor of the Meek can be an outlet as well.

Protection for your combo pieces are important. Riftsweeper should be included and Pull from Eternity only if you are dealing with a lot of exile effects. Silence has always been super helpful, and since there will be a lot of enchantment type effects you can consider running Greater Auramancy in conjunction with Sterling Grove . Sterling Grove also helps tutor for Carnival when needed.

The rest of the cards can be filled with either similar effects, interaction, or advantage.

Now going for your "Carousel" effect with Athreos. For this you would have to go with the infinite mana route, I would be adverse in going this route as it dilutes too much of the "Carnival" route. With the infinite mana you would need to add in cards like Phyrexian Altar , Ashnod's Altar , or Earthcraft in order for you to gain infinite mana. With that as well you need cards that will bring your creatures back to the battlefield or hand, so Phyrexian Reclamation , Corpse Dance , Disturbed Burial can be considered.

There can be probably more things I can think of but accept this short response before I take a more indepth look at it when I not sleepy lolol

Besides some of the high-end rocks and Imperial Seal , most of these things are in here (or in the side board). I was hesitant about the passive counter procs as most are higher cost. I left Champion of Lambholt on the for sure list (also a win con), but wasn't sure about ivy lane denizen as, for Ghave specifically he's great, but he wont be doing as much with the Carousel as most of my creatures are black.

Greater Auramancy and Sterling Grove, excellent call! These would be fantastic. Good call on Corpse Dance and Disturbed Burial as well, those would help tighten it up. I also appreciate the Earthcraft addition as, while I'll be getting infinite black with Carnival of Souls and most of my creatures will be free with Aluren , it'll be strong not just as an alternative, but as a way to get my deck moving with Ghave's creature production.

Thanks for the priority breakdown hkhssweiss! It'll help whittle everything down so I can focus on finer tuning.

No problem goldlion, Ivy Lane Denizen can still go in but can be the first to come out, it's only in there for Ghave, and plus the main point of your deck is to go for Carnival of Souls , so Ivy is just there as an enabler. Feel free to lemme know what else ya need! Always happy to help!

Land base wise, I don't think it needs to be said but just in case, while going for top tier cEDH the 9/3/3 split is the best while adding in alternative lands and the most efficient ones.

So in regards to that: The fetches excluding Scalding Tarn , the three duals Scrubland , Bayou , and Savannah . The three shocks Godless Shrine , Overgrown Tomb , and Temple Garden . That's the basic for a three color deck, next on priority is the pain lands which are Caves of Koilos , Brushland , and Llanowar Wastes . The multicolor land, Command Tower , Mana Confluence , City of Brass , Reflecting Pool . If going a bit more in since you are going to be running quite a bit of enchantments as well as creatures. Gaea's Cradle and Serra's Sanctum are decent inclusions, any land that gives you more than one is great. Ancient Tomb and Gemstone Caverns can also be considered.

Now I go back to sleep lol :p

A question of my ignorance, hkhssweiss: You said to add the fetches excluding Scalding Tarn . Why would I want to include something like Polluted Delta in here? Why not just use a basic swamp as I don't need the option to find blue and I'm not doing any land recursion/landfall triggers stuff?

Fetches adds in consistent color fixing, shuffle effects, and on the lesser part deck thinning. For example for a Sylvan Library trigger say they are all lands on the top 3 and you don't want to pay the full 8 life to rip it off the top, the fetch will help you reshuffle to have a new top 3 to look at. Works the same way with Sensei's as well.

In addition it also helps grabs our dual and shocks when you need them, it allows access for triple colored costs for example Necropotence or Geralf's Messenger . The deck thinning is also semi relevant as with most cEDH decks we are running a lower than average land count so not cracking a fetch will give us a slight higher chance of drawing lands when we need as well as not drawing a land after we crack one.

Hope that helps explain!

Also, Im wondering how much land we could get away with in here if the cmc made it down to 2.3?

If your going cEDH wise and adding in all the efficient mana rocks you can try going for 32-33 first and start from there~

Ah! that makes perfect sense in regards to the fetchlands. I definitely see the dual purposes and especially in regards to how the more competitive side gets into the subtlest percentages to give it that edge.