Welcome everyone to the new DLC summons game. The landscape is quite different due to how summons are "summoned" into the world. The technical stuff will be later on how it's not as powerful as before. Going to go over gear, mods, & traits first as well as where to get each one.

Applicable gear:
-Cultist set: Purchasable from Riggs or unlocked from class choice in tutorial. Allows for quick mod power generation to push summons out quicker.
-Elder set: Unlocked after a Yaesha siege event in Martyr's Sanctuary (Dungeon). Once a summon has been called; using a Dragonheart will buff that summons damage respectively to how many Elder armor pieces the player has.
(-Osseous set: No longer proc'd by summon attacks... RIP Osseous summoner)

-Soul Anchor: Unlocked in a Yaesha side dungeon Ahanae's Lament. [Increases duration of summons by 100% & increases wearer's Ranged and Melee damage by 5% per summoned minion.]
-Amulet of Epicaricacy: One of the rewards found by killing a Red Beetles in Corsus dungeons. [Increases Mod Power generation by 10%. When attacking an enemy with an active STATUS EFFECT, Mod Power generation is increased by an additional 25%.] i.e. if something is Burning you'll generation mod power crazy fast while the enemy is burning. Just shooting something else so you get the most burning time as possible.
-Vengeance Idol: Found in Yaesha as a random drop. [All damage dealt is increased by 30% when the wearer's Health is below 50%. Includes Summons.] If you don't mind health management this is a pretty great buff to have at all times.

-Soul Ember: Unlocked in Corsus dungeon Circlet Hatchery by destroying all Ixillis cocoons. [Summon Health is reduced by 60%. On death they'll explode dealing 150 plus weapon level damage within 4 meters. Summons that explode normally will deal 25% bonus damage.] Even though the tip says 150 plus weapon level damage the damage is the same from level 20 Sniper Rifle to a level 20 Submachine Gun.
-Soul Link: Discovered in Rhom in a cave near the Cryptolith red stone in Adventure mode. [Summons will steal 5% of the damage dealt and return it to the wearer as Health.] This is very good with Tentacle Shot & Seeker beetles.
-Gift of the Iskal: Unlocked in Corsus dungeon Strange Pass by killing the boss. [Mod Power is generated slowly over time, but reduces the wearer's Healing Effectiveness by 25%.] The penalty for this isn't much if you have Triage trait maxed out. Makes the -25% unnoticeable.
-Ring of the Admiral: Bought off Reggie for a heavy lump sum of scrap. [Damage received is increased by 300%. All damage dealt is increased by 15%. Includes Summons.] Wouldn't use this in online games with lots of lag.

-Melee weapon is whatever your preference. Recommend Guardian Axe.
-Guns: Curse of the Jungle God is unlocked after killing the Ravager in Yaesha. This pistol holds the boss mod Tentacle Shot, and is the only boss required to get a summon mod.

Mods
-Tentacle Shot (Max 2): Shoots an arching seed that roots into the ground making a tentacle. The tentacle does good damage and steals 2.5% of damage to each target as health for the player. This is a fantastic area of denial summon that punishes any enemies that get too close. Not effective against flying enemy types. A good strategy with these is to stand within the tentacles attack range to force mobs to get whipped when they approach you. Dodge within the tentacles to keep the enemies close.
-Beckon (Max 2): Summons a WASTELAND SKULL to seek out and attack enemies. The damage isn't as good as other summons, but these last much longer than other summons. These skulls are also a safe summon option with fighting bosses that use a lot of AoE attacks. Bosses usually can't reach them so you don't have to worry about summoning them every 10 seconds.
-Rattle Weed (Max 1): 50% Rattle/ 50% Weed. Always useful. Rattle Weed is an excellent way to remove aggro from you in a pinch. As long as you stop shooting with Rattle Weed is up. Soul Ember turns this summon into a pipebomb from L4D. Soul Link doesn't trigger from the Soul Ember explosion though.
-Rift Walker (Max 1): Unlocked by defeating the Dream Eater in a Corsus dungeon. The best panic button in the game for summoners. It's a Rattle Weed that takes longer to charge, and has a cooldown. In return gives you: 3 or 6 seconds of invulnerability, 3 seconds of 30% increased movement speed, and a large, powerful explosion that refills you health with Soul Link. Wearing Soul Anchor is what takes the duration from 3 seconds to 6. The "Rift" effect goes away after 3 seconds and you lose the movement speed, but you keep the invulnerability until the decoy explodes. It's Flicker Cloak, Rattle Weed, and Explosive Shot all rolled into one.
-Seed Caller (Max 2): Unlocked by defeating the Mangler on Earth. Great to finding ground based enemies went exploring. These ROOT HOLLOW will usually stagger lock mobs until death. Good mobile damage that you can forget about. Susceptible to elite/boss AoEs, and ineffective against flying enemies. If you want to stay behind cover these ROOT HOLLOW will do most of your work for you. Last note about these! Whenever they're about to attack something they will leap up to strike it. Be careful to not friendly fire them to death.
-Seeker (Max 3): Summons a BEETLE that rushes enemies and explode dealing great AoE damage within 4 meters. These are scurrying Dragonhearts when you have Soul Link equiped. They don't move as fast as other summons, but the explosion makes up for the movement impairment. Some might even consider them "cute". If you're able, summon these when a mob is bunched up or summon in the middle of a cluster of enemies. When the BEETLES explode they do so a foot or so in front of their target. Meaning that if you spam these at a distance they'll only blow up one enemy at a time...

Traits
Spirit: Mod Power Generation +25% [EX-CULTIST archetype or opening the locked safehouse with the MONKEY KEY in Sorrow's Field on Earth]
Arcane Strike: Melee Mod Power Generation +25% [Kill a world boss on Yaesha]
Blood Bond: Summons absorb damage taken by the player by 15% (When you get hit by something all of your summons die, but you take less damage. With Soul Ember they may just take something out with them.) [Acquired by activating the second Cryptolith]
Invoker: Summon Damage Bonus +20% [Summons kill 100 enemies]

Before the DLC drop summons damage scaled to the difficulty you where playing on. This would lead to folks steamrolling Nightmare cause summons where so powerful. This has been fixed/tweeted to keep summons damage on a steady curve of damage. Now summons have a utility based use which isn't a bad thing. Some summons excel at: wiping trash mobs, AoE damage, healing, spacing denial, or just constant damage to bosses. Even with all these roles, don't expect to be the primary damage dealer. Dare Devil Charm/Slayer set user is always going to do more damage than you. That doesn't mean that summons aren't crazy fun to run or useful :j I'm going to list a couple of summoner builds that I've run before and how each build style is played for ref.

Beetle Rusher:
I've got one piece of the Twisted Set on due to you running close enough to the enemy to melee if needed. Just another life steal option to keep you alive. The Deceivers Band gives you the free movement/evade speed you need to brush off mobs. The amulet of Epicaricacy is proc'd by burning folks with Spitfire then shooting someone else with the gun you have Seeker Beetles on. The primary gun can be whatever you feel comfortable with. The goal is to: build a couple of charges of Beetles, run through mobs, summon beetles in the middle, and blow everyone up. Seeker with Soul Link is very strong. If you blow up two enemies you'll get all of your health back. This is an unorthodox summoner build used for fun. The boss damage isn't stellar, but you probably won't die with all the life steal you've got. As long as you don't get "One shot" or stagger locked to death.


Rift Bomber:
Rift Walker panic button is really fun to use on mobs/elites. Tentacles are there if you feel like dropping them on your Rift decoy for extra damage on beefy enemies. They also double as a safety barrier between you & whatever made you use Rift in the first place. If you're playing on an easier difficulty then maybe run something other than Tentacle Shot, because the other party member will kill everything before enemies get close enough.

Vengeance summoner:
Use an AoE weapon (Hive Cannon/Pride of the Iskal) to self harm until Vengeance Idol activates. Really any combination of summons can work with V.I. I picked Iron Sentinel/ Seed Caller so I could back up to the turrets while the Root Hollows go out and damage. Could tag out Iron Sentinel for Beckon if you're running through areas.

That's a couple of examples of summoner builds but to be honest. Summoner builds have so many combinations I always adjust my summons to the situation I find myself in. I used those examples cause I usually see folks running the same summoner build over and over. Being able to bend your build will give you a lot of success where others might give up cause their "one build fits all" solution didn't pan out.

Thanks for taking time to check out this guide! Hopefully you found this helpful for informative. If you didn't that's fine too. If you have any off the wall summoner builds that are fun to run hit me up in the comments! Might just add it to the list of examples ^^ Good night!