I would cut Gilded Lotus for Expedition Map .

Being able to fetch Nykthos, Shrine to Nyx . when you play this spell its gonna be better than Gilded Lotus because that land can make way more mana than gilded lotus. Also it's harder to remove. And when you already have Nykthos, Shrine to Nyx , just fetch Hall of Heliod's Generosity or Emeria, The Sky Ruin .

Also sweet background but I think Hall of Heliod's Generosity is more on flavor. I really dig this deck man. It's kinda how I would have built it too

I couldn't find hall of heliod art at a good resolution

Felidar Sovereign for the free wins.

I have actually removed felidar because my play group stops at nothing to kill or counter it. So test of endurance is what I run now. Because generally they forget about it.

i suggest Crested Sunmare

Crested Sunmare

So for a bit I had removed sunmare because I felt it wasn't doing too much but now that I have the soul sister package I should probably read it. But for what? I really like the list where it is at.

If your Walking Ballista gets countered or removed. Sunmare would be able to be protected with Mother of Runes type of effects, that could be a alternate way to win. You are right though, the deck is fine as is. I just think Crested Sunmare would be a good backup. It would work really well since you could gain life on their turns to.

Cut Hero of Bladehold and Brimaz, King of Oreskos for Serra's Sanctum or a Plains and Crested Sunmare

This is a cool deck! Have a +1. I've been trying to build a similar deck as well, so here's some suggestions/food for thought, although I don't know where you would put these because your deck is already built well.

• Darien, King of Kjeldor - Even though he is 6 cmc, if you have him out with a soul sister or similar card you essentially take no damage (or gain life) from attacks, etc. and make lots of tokens. Pairs well with cards like Ancient Tomb .

• Pariah - More of a gimmick, but put this on Heliod (indestructible) and you can't take damage.

• Elesh Norn, Grand Cenobite - She's just good.

• Phyrexian Rebirth - If you really need to wipe the board, this leaves you with something afterwards.

• Dusk / Dawn - Similar to Phyrexian Rebirth, it doesn't destroy your soul sisters, etc. in the first place. Also, if the soul sisters have died, you can return them to your hand with this.

Cathars' Crusade can also get out of hand very quickly, and Winds of Abandon is a one sided board wipe which lets you easily swing for lethal if you haven't set up the Walking Ballista combo or if you opponents managed to stop it.