At Mastery Rank 3 you gain access to Syndicates. By gaining rank with a syndicate you will be able to buy augment mods for your warframes and weapons. You will also be able to buy some weapons, that are special versions of some standard weapons.
Some of the syndicates are allies, some are neutral and others are enemies. When you gain rank with a syndicate, you will also gain a percentage of that with their ally - but you will also lower your rank with their enemy! Ultimately the enemy syndicate will try to kill you by sending a squad of elite units after you in any random mission you do (sort of like when you are marked by the Shadow Hunter after killing certain a boss).
It is possible to choose 3 syndicates without conflicts - either select:
- Steel Meridian / Cephalon Suda / Arbiters of Hexis - or
- Red Veil / New Loka / The Perrin Sequence
Any other mix will result in you gaining rank with one syndicate while also lowering rank with another you are trying to level...
Each syndicate has some background story and ethics but you should really just ignore that and instead select a syndicate based on which warframe or weapon mods you can buy from them. Personally I would recommend selecting Steel Meridian / Cephalon Suda / Arbiters of Hexis as they provide augment mods for the warframes I consider most essential.
The Steel Meridian syndicate provide augment mods for these warframes:
- Atlas / Ember / Excalibur / Frost / Khora / Mesa / Nezha / Nidus / Nova / Oberon / Rhino / Saryn
They also provide the powerful Scattered Justice augment mod for the Hek shotgun that gives up to 200% Multishot + 1 Justice point. When 2000 Justice points are collected by killing enemies with the Hek, it will deal 1.000 AoE Blast damage to nearby enemies + restore 25% of your health + temporarily increase your armor by 15%. This is a great augment mod!
You can also buy a few special weapons including the Vaykor Marelok / Vaykor Hek / Vaykor Sydon.
Arbiters of Hexis
The Arbiters of Hexis syndicate provide augment mods for these warframes:
- Ash / Equinox / Gara / Harrow / Inaros / Limbo / Loki / Mirage / Nyx / Volt / Wukong
You can also buy a few special weapons: Telos Akbolto / Telos Boltor / Telos Boltace.
The Cephalon Suda syndicate provide augment mods for these warframes:
- Banshee / Chroma / Frost / Hydroid / Ivara / Limbo / Mirage / Nezha / Nova / Octavia / Vauban
You can also buy a few special weapons: Synoid Gammacor / Synoid Simulor / Synoid Helicor.
The Perrin Sequence
The Perrin Sequence syndicate provide augment mods for these warframes:
- Banshee / Chroma / Inaros / Ivara / Mag / Nekros / Nidus / Rhino / Trinity / Valkyr / Vauban
You can also buy a few special weapons: Secura Dual Cestra / Secura Penta / Secura Lecta.
The Red Veil syndicate provide augment mods for these warframes:
- Ash / Atlas / Ember / Harrow / Khora / Loki / Mesa / Nekros / Saryn / Titania / Volt / Zephyr
You can also buy a few special weapons: Rakta Ballistica / Rakta Cernos / Rakta Dark Dagger.
The New Loka syndicate provide augment mods for these warframes:
- Equinox / Gara / Hydroid / Mag / Nyx / Oberon / Octavia / Titania / Valkyr / Zephyr / Wukong /
You can also buy a few special weapons: Sancti Castanas / Sancti Tigris / Sancti Magistar.
The following syndicates are neutral i.e. raising rank with one of these will not lower your rank on any of the other syndicates.
- Conclave is a syndicate where you earn rewards for PvP battles.
- Cephalon Simaris want you to scan targets to earn rank. He sell the very useful Energy Generator mod for the Dethcube sentinel and also a key for getting access to the Simulacrom, where you can safely experiment with different weapons and mods against all the enemies you have previously unlocked by scanning them.
- Ostron are the inhabitants of Cetus - the big city leading to the Plains of Eidolon on Earth. You can earn rank by doing bounties or by selling fishing and mining and selling what you collected for rep.
- The Quills are also located in Cetus. You earn rank by selling Sentient Cores, that are obtained by killing sentient enemies on Plains of Eidolon. This is where you can buy an Amp or Arcane for your operator.
- Solaris United is a new syndicate that will be introduced when the Fortuna update goes live...