I am currently looking to build an Eldrazy Aggro (not X-Post) list, to be used mainly in multiplayer (typically 3-player FFA or 2HG).

I'm looking for ways to complete the following baseline :

// Lands : 25
3 City of Traitors
4 Ancient Tomb
4 Eldrazi Temple
4 Eye of Ugin
10 other : Cavern of Souls, Wasteland, Basics...

// Eldrazis : these 22 are locked in
2 Endbringer
4 Eldrazi Mimic
4 Endless One
4 Matter Reshaper
4 Reality Smasher
4 Thought-Knot Seer

// Spells
2 Umezawa's Jitte

That's 49 slots. I'm looking for ways to complete this list while keeping it Legacy legal (shouldn't be too much of a restriction...).

As a reference, a typical non-colored single-player Legacy list would complete the deck with
2 Walking Ballista
4 Chalice of the Void
3 Simian Spirit Guide
2 Dismember

I can envision completing the list in different ways, but there are a lot of cards I am "defaulting to", for lack of better ideas.

Colorless

Compared to the Legacy list, CotV can be out, since Chalice is far weaker in multiplayer (with games going longer and lists being more top-heavy). I'd remove SSG too. I can switch the 2 Dismembers for 2 All is Dust. Adding 4 Thorn of Amethyst seems easy, hosing everyone else. Ballista could stay but it's more because I am lacking inspiration. So the 11 non-land slots are :

2 All is Dust
4 Thorn of Amethyst (?)
2 Walking Ballista (?)
3 ???

I'd also appreciate ideas on what lands to finish the mana base. I could go 4 Cavern / 4 Wasteland / 2 Mishra, but if there are other interesting possibilities, I'm all ears.


Blue splash

The blue splash opens up Rhystic Study, which is a card I always love to play, if only for the pleasure of being that annoying guy asking "do you pay 1 ?" every time anyone does anything. Plus, it would combo well with Thorn of Amethyst.
For the same reason I have not kept AS& SS in the green option, all turbo-xeros cards like Ponder etc are not considered here, as the deck is consistent enough already.
Here again no idea barring 'default' cards : Cyclonic Rift, Fact or Fiction (not needed if Rhystic Study), ... ?

4 Rhystic Study
4 Thorn of Amethyst (?)
2 All is Dust (?)
1 ???

Green splash

A green splash could be used for things like 4 Ancient Stirrings and 4 Sylvan Scrying. I was initially just going to go this way (I am used to value consistency-improving cards very highly) but my experience with the single-player Legacy version of the deck is that it is in fact already very consistent as-is. There's effectively 11 sol lands already and that's about the only thing you need (well, that and a couple of the 22 Eldrazi the list packing).
The only good options I'm seeing left in green would be things like Duskwatch Recruiter or Sylvan Library (to help refuel if needed) and the universal utility Beast Within.
3 Beast Within
2 Duskwatch Recruiter and/or Sylvan Library
6 ??? (could be 2 All is Dust and/or 4 Thorn of Amethyst)

Black / White / Red splashes
Here I have no idea at all barring generic "good" cards.
Black : Blood Tithe, Kokusho, Phyrexian Arena/Bloodgift Demon ? With 3x Urborg, Tomb of Yawgmoth in the manabase.
White : 4x Thalia to combo with 4x Thorn of Amethyst
Red : World at war, Berserker's Onslaught, Fiery Confluence

What are your thoughts ?