Strategy here is quite simple : Bolas wins, everyone else lose. Basically an alternate ending of the War of the Spark.

How it works : Nicol Bolas, Dragon-God -8 make everyone but you lose the game. NEAT ! But how can you EVER go to -8 if you're such a threat ?

This is where The Elderspell comes up. You can abuse the fact that everyone around you MIGHT play a planeswalker, because you know... Oathbreaker... And then kill it. Every planeswalker killed by The Elderspell will give Nicol Bolas, Dragon-God 2 additional loyalty counters.

With a way to consistently win the game and destroy every planeswalker around the table in the command zone you have to focus on simpler things :
1- Deny stuff.
2- Kill stuff you can't deny.
3- ???
4- Profit.

1- Counterspells.

Probably the best way to enjoy losing friends. They are here to keep you safe from harm.

Some of them (Flusterstorm, Miscast, Spell Pierce, Countersquall, Izzet Charm, Force of Negation) can't counter evey spells, but it's ok, your goal is avoiding bad surprises like Hero's Downfall which can deny YOUR fun at instant speed. They are both the cheapest and most efficient counterspells considering evey other player also got an instant or sorcery in command zone.

Some others (Counterspell, Disallow, Ionize, Supreme Will, Force of Will) can counter everything, but you should keep them for direct threats to your wincon (aka Nicol Bolas, Dragon-God)

2- Wraths.

With 3 other players around the table you just can't counter everything they got. But you can KILL eveything they all collectively played last turn with the right spell, achieving the same objective.

Spells like The Meathook Massacre, Toxic Deluge, Damnation, Hour of Devastation, Blasphemous Act can wipe out the board. They also are the reason we don't play creatures : we'll consistently clean the board to make sure our Nicol Bolas, Dragon-God is safe. (Force of Despair might seems weaker and can be changed by another similar spell like Yahenni's Expertise or Mutilate but it's a quite cheap spell and can be played at instant speed.)

Other spells like Torment of Hailfire, Dark Intimations might not be as effective but they serve the same purpose and helps a little bit somewhere else (Torment of Hailfire in particular might even be considered in the command zone)

3- Mana and draw.

We want to get our wincon as fast as possible but Bolas is a pain : 5 colored mana including 3 black mana while most of our spells are either blue or red...

We'll then play the cheapest mana rocks possible : Arcane Signet, Obsidian Obelisk, Talisman of Creativity, Talisman of Dominance, Talisman of Indulgence are quite efficient 2 generic mana each, meaning you'll always have a way to play them.

We can also cheat a bit of last second mana : Strike It Rich allows us to change a red for a blue or black mana or a mana next turn. Lotus Petal can gives us a quick boost to cast Bolas on turn 3.

Card advantage is also quite important : Seize the Spoils, Big Score, Pirate's Pillage, Unexpected Windfall might seems expensive but they all give us some mana back (sweet sweet treasures). Allowing us to cast some counterspells or play Bolas faster.

Dig Through Time, and Treasure Cruise are supposed to be cheap by "optimizing" the many spells that will end in your graveyard, but they can be discarded for the red draw spells early in the game (or used as cannon fodder for Force of Negation or Force of Will).

4- About the manabase.

We've got here a quite efficient (but expensive) manabase, most lands comes in play untapped, are flexible (Blightstep Pathway // Searstep Pathway, Clearwater Pathway // Murkwater Pathway, Riverglide Pathway // Lavaglide Pathway), filter our manabase (Cascade Bluffs, Graven Cairns, Sunken Ruins) or allows us to get the most land cards out of our library (Bloodstained Mire, Polluted Delta, Scalding Tarn). Some are even counterspells with benefits (Jwari Disruption // Jwari Ruins).

Most of them can be replaced with cheaper alternatives ofc.

5- The forgottens.

I haven't spoked about a few cards :

Deliver Unto Evil - Useful to fill your hand with already-used counterspells or wraths.
By Force / Vandalblast some artifact hate is never bad, you want to ramp, but if you can stop your friends to do so you should.
Settle the Score is a surprise (at sorcery speed tho) way to deal with some annoying indestrucible stuff. And it gives Nicol Bolas, Dragon-God 2 more counters !

6- The considered.

60 is too few to put everything but some cards should be considered :

• Leyline of Anticipation Bolas is scary but bolas at instant speed ? Wraths, card advantage,... everything is scarier when you can play them during opponent's end steps.
• Ashiok, Dream Render / Chandra, Acolyte of Flame / Dack Fayden / Karn, Scion of Urza / Kasmina, Enigmatic Mentor / Liliana of the Veil / Narset, Parter of Veils / Saheeli, Sublime Artificer, mostly cheap and quite efficient on their own... And also they can be sacrificed to Bolas if you opponents refuse to play their own planeswalkers (but don't tell them :( ) You can swap to a more planeswalker-oriented strategy. Most of them are able to pump up creatures which is even better when you realise Nicol Bolas, Dragon-God can also copy theses capacities of needed.
• Cyclonic Rift a bit expensive to cast overloaded but guarantees a win if Bolas is on the field.

Fun fact : When I first built this deck TCG player estimated a 1337,69$ cost. Idk what to do with this information but I had to share it.