This build revolves using Ultron's summon abilities to snapshot a buffed army that persists with you through multiple fights. The only non-summoner choice we make is to take the talent that turns Energy Overload into a nuke, helping patch the weakness of Summoner Ultron, his clear. With a good clear in EO and a million summons, Sumtron finally can stand up and compete against the other Ultron builds.

This build automatically calls in an army of summons at first combat, so the most important moments are the first few seconds before you engage. We want to use Energy Overload into nothing to trigger Cybernetic Implant, and then start combat with our signature We Are Ultron. This means we enter combat with great buffs up, and all our long lasting summons will snapshot these buffs and come in giga buffed. Then, you simply hit buttons as they rotate off CD and enjoy the summoner playstyle.

Skill Explanations:

 - Filler. Use when you don't have anything else to do.
 - Vulnerability, get this up ASAP, also triggers our Power Doop (Phys).
 - Damage on a 8s CD, decent damage.
 - Damage on a 8s CD. Kinda dumb AI, best used when trash is cleared.
 - Damage every 8s, but most importantly your summon control skill. This commands them, overriding bad AI!
 - Damage every 6s that empties your Power, triggering Cybernetic Implant. This is also a reliable player controlled clear, allowing you to deal with adds while your summons are directed via Operation: Swarm to hit the bosses.

Rotation:

As mentioned the seconds before combat are some of the most important. Using Energy Overload into nothing to trigger your Cybernetic Implant but NOT getting you in combat, and then initiating combat with your signature We Are Ultron will give you the best army to start with. As they die, they'll cycle back in but you should have Cosmically Enhanced Crossbones's Teaching Credentials rolling as well as other combat buffs. Maintain Operation: Annihilate up for the vulnerability, and otherwise you're hitting buttons as they rotate off CD.

Gearing:

Gearing wise we're just rounding out our kit with solid stats and a general build. A reminder for returning players used to old Summoner Scaling, in 2.16a summons scale off player stats. This is a helpful wiki article explaining it, but TLDR if you gear for your hero you'll in turn buff your summons, think of +Summon gear the same as +Ranged.

Artifacts: 
 is a great alternative, providing good rounded stats and a summon specific boost on a hero that has a majority of their skillbar with summon tags.

 All can work as well.

For rings: Sling Ring of the Kamar-Taj (energy) will help a lot early in the gearing journey, as it provides some nice CritHit and defensive stats. Ultron will feel squishy, and when you start losing your summons (maybe a boss AOE pops them), it can feel like youre on your backfoot a lot. Sling will help, and eventually a high damage cosmic ring will be your BIS. 

For Slot 4: I believe a Cosmic S4 might be competitive with Cerebra, but the ease and stat assurance of a Cerebra makes it an easy Slot4 for Sumtron.

Legendary: We run an i80 Trident for the great stats and (comically) the summon health. Since we're snapshotting such powerful summons to start, keeping them up and around longer helps a ton. Also, we really dont want them to die to minor things and leave us stranded.
If youre using i70 Legendaries, I'd suggest using Gungnir for all your hero i70s. If you find your summons are dying too often with an i70 Gungnir, this might be one of the few exceptions to go i70 Trident.

The priority for insignias is less the base, and more the rolled affixes. We really value CritDam and CritHit. Overall our prio is CritDam>BrutStrike>CritHit>>>>RangedDam.
Brutal Damage isn't great for insignias due to how low it rolls compared to its usual stat weight. 1000 CritDam is worth twice the weight of 1000 BrutDam.

Catalyst would be Invis / LifeOnHit / Spirit on Medkit / Energy ideally. There is a choice to be made here with +1000 Damage on Signature or Medkit Shield. With Snapshotting, that +1000 will carry into our summons for a very long time. That said, I'd advise medkit shield to start, and when you feel comfortable with Ultron and the kit maybe look into swapping to a +1000.

Talents Explained:

Row 1: We begin growing our Army.

Row 2: Legion is our main summoner pick here, giving our kit a bit more oomf.

Row 3: Calling in more combat summoned minions, raising our army to 6.

Row 4: We are giving up Relay Target Coordinates to boost Energy Overload. EO gives us the clear and power dump we want for a smoother gameplay experience. If you want to run Relay Target Coordinates, swap out Cybernetic Implant for Ultron's Cosmically Enhanced Encephalo-Beam.

Row 5: Shorter sig and bigger buff. Works the best for us.

Infinity Points:

Order is up to preference, but I'll highlight getting 150pts in the different gems at the overall priority. Reminder that every 150 is a big +1 All Attributes stat bump, so chase those to start on an early account, but dont go into gems with non-worthwhile stats just to get a 150.

I usually prefer to start with 152 in temporal for the extra dash and QOL movespeed/attackspeed, then 150 energy or 150 dura if the gearing is lacking, or 150 CritDam/BrutDam if you feel solid gear and base damage. The infusions and 0.6% (rounds up!) Crit% and Brut% are small fillers you can take along the way, reskilling when you can hit a 150 checkpoint.

Videos & Gameplay