PoB:

https://pobb.in/Eu6umCzBRLau

Taking heavy inspiration from a build by u/pyrvuate, this is an adaptation of a ballista Elemental Hit build for the Phrecia event. Paladin seemed to be the best choice for tri-elemental attack builds due to Elemental Relic and 25% increased damage taken.

It can reach 30M dps while being reasonably tanky, with 19k phys and 55k ele max hit which is enough for T17s with not too scary map mods.

Offense:

• Piscator's Vigil is a great driver for the build, making the most out of Wrath + Anger + Ele Hit of the Spectrum's massive flat damage (unfortunately, we get 0 benefit from Hatred aura).
• We use Paladin's increased elemental damage taken node, as well as the taunt node for increased damage taken. With the taunt node, are also able to use Enduring Cry (for brutal charges) and Battlemage's Cry to full effect, and allow for permanent rage.
• The rest is standard crit and ailment stacking for Ele Hit through Secrets of Suffering + Skitterbots.
• Our crit is solved by having high base crit from the wand + Battlemage's Cry + Brittle.
• An Anger-buffed Lightning Golem will be able to occasionally ignite for a total of 6 ailments (not a pob-only thing swear).
• Because charge generation is scuffed on totem builds, we use Ralakesh + Arn's because that combo is just unbelievably broken for its cheap price.
• The clear weakness of Barrage support is mitigated by having the totem setup, allowing for decent clear with great single target without gem swapping.

Defense:

• Our main defenses make use of combining the Paladin and Champion's (through Forbidden jewels) taunt nodes. Their defensive buffs are applied by the totems, stacking for a total of ~46% less and 10% reduced damage taken (I assume they stack, I don't get one-tapped by phys hits so it probably works :p).
• We are also ailment immune due to Purity of Elements (which also helps our totems be tankier).
• Because investment into regen is hard to get, we solve it by using Trolltimber Spire and instant leech.

Overall, build is leaguestartable (I used a bow after I bought the trans gem at Act 5 and swapped to wand and ballistas at yellow maps), sorta cheap to scale (not at day 1-3 though) but extremely gem and passive point starved. Your biggest upgrades are Secrets of Suffering, a 20 quality Ele Hit, Ralakesh + Arn's, and Ashes.

You can make it a lot more defensive if you want by fitting in Flesh and Stone, some max res in body armour + watcher's eye, using a warcry cluster instead for Warning Call + Lead by Example, and eventually using Progenesis.

Slayer build ( u/pyrvuate ):

https://www.reddit.com/r/PathOfExileBuilds/comments/1etv0nw/ele_hit_of_the_spectrum_ballista_totems_slayer/

Why wand ballistas and not bow?

The wand projectile is 100% cooler than the bow projectile of Ele Hit.