(This guide will be cleaned up a little later, still making edits and testing stuff.)

New Venato build to go with this build as well! https://overframe.gg/build/258984/

NEW Meta Caliban Build, for people who are looking for something stronger / more synergistic than this Build: https://overframe.gg/build/265878/
The reason I released the build listed above is for those people who don't want to play a summoner playstyle but are still looking for a solid build. After reading over some comments, I realized people may want another good guide for synergy between his abilities. That being said, this build continues to be what I believe is the best Summoner [Caliban] build.

IMPORTANT NOTE: It has been confirmed that [Caliban]'s Passive and [Adaptation] do not stack. If you equip [Adaptation], you will gain the higher of the two resistances, effectively losing you [Caliban]'s passive on yourself. For this reason, in my [Caliban] builds, I prefer to treat his passive as a free [Adaptation] that takes up no mod space, that is why it is not on this build.

To begin with, [Umbral Intensify], Transcient [Fortitude], [Augur Secrets], [Power Drift] and [Energy Conversion] are all here to give us more Ability Strength. Conculysts Level and Damage scale to your Ability Strength, so having it as high as can be is a must. We don't use [Blind Rage], as this frame already has high costs and we don't run any efficiency mods. [Energy Conversion] makes it so that as long as you pick up an energy orb before casting Lethal Progeny, you get a huge buff to your Conculysts.

If you don't want to use an Umbral Forma on this build, that is perfectly okay. Replace [Umbral Vitality] with [Quick Thinking]. You will lose a little bit of strength, but will maintain the overall power of this build.

Our Aura is either [Corrosive Projection] for High level content, or [Energy Siphon] for lower level content. Either one is good.

[Narrow Minded] and [Primed Continuity] take care of our Conculysts duration needs. These both should keep the Conculysts around for about a minute each.

[Primed Flow] is for a higher energy cap.

Finally [Umbral Vitality] is here to make sure we don't go down to a random toxin proc or something, as well as to pump up Umbral Intensify.

Arcanes can be whatever you want, I like Energize/Molt Efficiency. With this new Arcane, the Conculysts can stay up longer than ever before.

So, to actually play this build, it's pretty simple. Razor [Gyre] can be replaced by Empower, or any other Helminth Ability of your choice. Empower stacked with [Energy Conversion] will make your Conculysts about level 104, which is the perfect level for steel path mission runs. (Credit to Alexicon for testing Empower). From there, use Sentient Wrath for CC, Fusion Strike for Armor Strip, and Conculysts for Damage and Support. These guys can be used for Shield Gating and at this level should hold up in the higher level content very well. Make sure you try to pick up an energy orb before each cast of Lethal Progeny, and try not to cast other abilities before Lethal Progeny once you have picked up an Energy orb for best results.

If you want to make any changes to the build, I recommend replacing [Augur Secrets] with another Augur mod, like [Reach] or Message, to fit your goals for the build. [Reach] helps the build be less dependent on the Conculysts and Message just buffs up their duration even more.

Update Veilbreaker:

With Archon Shards, this build can now be even better than it was before. Until Overframe allows you to put Archon Shards in builds, it will remain the same above, however we can now run Archon Shards to give us Ability Duration or Ability Strength. Going Ability Duration allows you to remove [Narrow Minded] and Molt Efficiency, and run an Ability Strength Mod and Molt Augmented instead. Going Strength means you can have a much higher conculyst level.