This is a deck I built for a friend on Fiverr. If you want a deck built, you can find me on Fiverr as genoslugcs. Check me out.

The Deck

Ok, so I think this checks most of the boxes in terms of what you wanted from the deck. We have Omniscience to cheat things out, several ways to ramp into the more expensive stuff, 12 Planeswalkers, and Carth the Lion to make several of them able to ult the turn they enter. There are also some proliferate cards that can help add counters as well. Here's a look at the moving parts in some more detail.

Carth the Lion

Carth is exactly the type of card you want to play in a build like this. First, he digs for Planeswalkers when he enters the battlefield or when our planeswalkers die, which is very strong. And as mentioned, he makes some of the walkers in the deck, Nissa, Vital Force for example, able to ult the turn they enter. There are several others, such as Liliana of the Veil, which can ult the turn after they enter.

It's worded slightly strangely, so here's how it works. Your loyalty abilities cost one less (or add one more) loyalty. Take Liliana of the Veil, for example. The +1 becomes a +2 with Carth on the battlefield, while the –2 becomes a -1. So, with a Carth out, we can ultimate Liliana of the Veil with just five loyalty. Another example would be Nissa, Vital Force - She comes in with five loyalty counters. With Carth out, her ultimate (usually six) only costs five.

Now, let's move onto the ramp.

Ramp

Carth isn't exactly the definition of cheap to cast in Modern. And Omniscience definitely isn't. So, we're going to need some major ramp. I found the combination of Utopia Sprawl (to make forests tap for double) and Arbor Elf (to untap an enchanted forest and use it again) to be the most effective. That said, I couldn't not add Delighted Halfling. Not only does it tap for any color when casting legendary spells (Carth and all the walkers), but it makes them unable to be countered as well.

I had no problem with producing a ton of mana in testing and could cast Omniscience as early as turn five.

The Planeswalkers

As of now, I have three of each walker pictured above, and that seems to work well. Remember that Carth digs pretty deep for Planeswalkers. The abilities of Nissa, Vital Force can be game-winning. The plus +1 making a hastly 5/5 is quite hard to deal with later in the game. And the emblem from her ult stays on the battlefield forever, drawing cards. I didn't use her middle ability at all, but I imagine there would be times you could use it to buy back Carth.

is a classic and pulls a lot of weight in controlling the board. With Carth in play, she can ult the turn after she enters. If you've never been on the receiving end of the ability by the way, it's pretty much game over. And again, anytime you do ult and kill a walker with Carth in play, you'll dig for a replacement.

The second Lili to make my list is Liliana, Dreadhorde General. She's really a jack-of-all-trades type card in the deck. She draws cards, she makes creatures, she removes opposing creatures, and can really annihilate the board with her final ability.

Lastly, we have Karn, the Great Creator. He's important to the deck in two ways. First, he coincidently shuts off a ton of artifacts, which can be nice. Secondly, and most importantly, is his -2, which can tutor cards from the sideboard. This is always good, but being able to do it as a -1 makes it even better. Here is a look at the backbreaking silver bullets he can get from the sideboard.

• Damping Sphere - Hates on special lands, storm, burn, and anything else that wants to chain spells together.
• Elixir of Immortality - Life gain
• Engineered Explosives - Wipes the board
• Ensnaring Bridge - Stops creature-based aggro
• Liquimetal Coating - Works in conjunction with Karn's +1, making opposing lands 0/0 creatures, thus blowing them up.
• Pithing Needle - For opposing Planeswalkers, or other activated abilities
• Tormod's Crypt -Graveyard Hate
• Void Mirror - Stops Eldrazi, much Tron, and all free spells like Cascade.

This wish board makes the deck much better equipped to deal with opposing decks, considering that the main board is devoted to the planeswalker package. That said, I did get some mainboard interaction in, and it supports the main theme via proliferation.

Interaction And Proliferation

Drown in Ichor is a phenomenal removal spell for the deck that also adds fuel to whatever Planeswalkers you have in play. With a single proliferation every walker in the deck can use their final ability the turn they enter. So, these spells pull some major weight in the deck.