Stellaris Nemesis introduces new features for the end game Crisis, including the chance for the player to become the Crisis. Alternatively the more diplomatic player may connive to have himself elected to be the Galactic Custodian to lead the Galactic Communities’ response to the Crisis.
To become Galactic Custodian is the pinnacle of a long climb up the Galaxy’s greasy pole of space politics. The crucial resources for succeeding in this are Diplomatic Weight, Favors and Influence. It also helps a lot to have good relations with other members of the Galactic Community, especially those with substantial Diplomatic Weight themselves. Friends in high places.
For obtaining Diplomatic Weight, Favors, Influence and good relations our primary tool will be our Envoys. The more we have of them the better.
Here follows an empire build optimised for becoming the Galactic Custodian. It is also a great build for a game making deep use of Federations and the Galactic Community features introduced with the Federations DLC. The key power of this build is the power of diplomacy and politics with a side hustle of espionage. For this reason it may be known as the Diplomat Build.
Naturally we will want Diplomatic Corps for one of our two civics. This will give us an extra 2 envoys which are so critical to the Diplomat’s strategy. It also buffs our Diplomatic Weight.
For the second civic I would go with Cutthroat Politics. This buffs our Codebreaking and also reduces the cost of edicts. The former can help our envoys obtain favors even from enemies and the latter benefit can save us precious influence. There are a number of Edicts that have great use to the diplomat.
For ethics Fanatic Xenophile is another natural choice. It also gives us extra envoys as well as a bonus to trade value. The bonus to trade value is more useful that it might seem at first. Being a member of a Federation has a cost, though it is not easy to see from the User Interface. The cost is 15% of our energy budget, but it is not taken from the energy we get from trade value only that harvested from resources or jobs. This means if we form our economy in such a way as to get out energy from trade rather than generator districts etc we can get out Federation membership on the cheap.
Another useful benefit to Xenophile is a positive opinion modifier with most other empires.
For the second ethic there are a few that might also work well enough but I have gone with Pacifist. The others to consider would be Spiritual and Egalitarian. Pacifist plays well with a strategy we will use to maximise the pops we have and their happiness. This is to maximise our Diplomatic Weight, see the section below on Diplomatic Weight.
For government type I have gone with Imperial for the extra edict slot but others can also work. We want to build up a big population for the Diplomatic Weight so the discount on population sprawl from Dictatorial is helpful. Oligarchic dishes out more precious Influence from factions which is also good.
I have formulated the species traits to make our primary species the perfect host in order to help maximise immigration and so our population size and happiness. Charismatic gives us extra amenities from jobs. Extra amenities will make our clerks and entertainers especially effective at keeping our pops happy and drawing in migrants. All of which will help us build up diplomatic weight. Since entertainers also make unity we can also take Traditional for a bit more of that. Alongside our entertainers we can also have culture workers who produce unity and society research. Natural Sociologists will give us a bit more society research. A lot of important techs for us are in the Society tree so that helps too.
To balance those benefits with a negative trait I would choose Non-Adaptive since it is virtually a free of cost given the Origin I would choose.
A galactic custodian should have an impressive capital, not least because if he manages to convert his custodianship into becoming Galactic Emperor (with thunderous applause) that capital will be the capital of the whole galaxy. Moreover since Diplomatic Weight is heavily built on happy pops we quite want a high capacity capital with universal habitability to house them. For these reasons I believe a Ring World Origin is best.
Of course it is a long grind to get the Mega-Engineering tech needed to open up the ruined sections of the Ring World but even just the starting section can potentially house and employ 200 pops.
To become Galactic Custodian one must win a vote on a resolution naming us for that role. To win that election naturally one must have good relations with as many as possible and perhaps favors to call in too. But before one can even be eligible for that election one must be on the Galactic Council. To get on the Galactic Council the only thing that matters is Diplomatic Weight not popularity.
Initially the Galactic Council is formed from the top three powers in terms of Diplomatic Weight but there are resolutions that can expand or contract that number. If you are in fourth place for Diplomatic Weight you might put forward or support a resolution to expand the Galactic Council. If you are in second or first place you might want to shrink it.
Diplomatic Weight has its uses in getting our way in the Galactic Community and even for dominating a Federation but its crucial role here is to make us eligible for the Galactic Council.
Diplomatic Weight is calculated from combining fleet power, economic power, technologies, the number of our pops with certain multipliers from civics, techs, resolutions and edicts. Envoys assigned to the Galactic Community also contribute a multiplier to our Diplomatic Weight, 10% for each one.
The sheer number of pops we have is not so important as their happiness. A maximally happy pop is weighted three times as much as a maximally unhappy pop or a robot. A few happy pops will do as much for our Diplomatic Weight as many unhappy ones.
This is where happiness boosting gambits can really help us, for example running the Social Welfare or Utopian Abundance (if Egalitarian) living standards.
Our strength is not really in tech, fleet building, economics or pop growth though. Our strength is in diplomacy, so we shall leverage our diplomacy to turn our otherwise mediocre talents in tech and economics into strengths. Our envoys can win for us Commercial Pacts, Research Agreements and Migration Treaties which increase the power of our economy, research and population growth respectively. If we have more such agreements than anyone else then that will be our edge in these fields.
Most resolutions, if passed, will come with a multiplier or penalty to diplomatic weight for certain aspects of an empire, like fleet power, technology, pops and economy. So one use for manipulating which resolutions are passed and which fail is to translate them into still more diplomatic weight for ourselves at the expense of our rivals.
For example if we are the leading power for technology it will help our political power to get resolutions passed that increase the diplomatic weight attached to technology and block those that apply a penalty.
Since our important strengths are envoys, edicts, influence and favors we are quite at liberty to play the Diplomat Build tall or even very tall rather than wide.
See this strategy guide to tall vs wide playstyles in Stellaris.
Of course Diplomatic Weight is affected by the number of pops too and pops add to our sprawl. So we do have an interest in growing our pops despite the sprawl cost. However even here quality vs quantity counts because the happiness of pops is weighted rather more than just the sheer quantity of them. As a rule of thumb, one happy pop is worth the diplomatic weight of 3 robots.
In my playthrough of the diplomatic build, at the point I converted my custodianship into becoming Galactic Emperor my faction directly owned no more than 8 systems.