Jungroan's Poison Spectral Helix Assassin (Tree highly optimized by me, without changing any of the budget gearing). Complete with new leveling progressions from Level 2 to 95 and everything in between.

Basically as the title states. I took Jungroan's WiP PoB for a Poison Spectral Helix Trickster (or what supposedly is, I can't actually source the PoB outside of a link from this sub and word of mouth) and swapped it back to Assassin simply because the eHP is about the same (but without the overleech and various other QoL sustain), but Assassin still does more than 2.5x the DPS with the right tree. I then adjusted the tree in quite a few places to squeeze out as much DPS as physically possible without sacrificing any of the original defenses (outside of being Assassin instead of Trickster). I've also included leveling trees from 2 to 95.

Things to note: The Covenant is not likely to be cheap early on, as much as people are hoping it's going to be. It more than triples our DPS, which is why I'm opting for Assassin instead of Trickster, to much more easily get over DPS plateaus, by gearing and tree-pathing easier with 40% poison chance from Ascendancy, and hitting crit-cap with less effort considering Toxic Delivery. Do also note that the DPS here is a bit fluffed considering I have Vaal Haste and Focus up, so consider your burst DPS and temper your sustained dps expectations.

With all that said, here you go, and I hope some people find this useful: https://pobb.in/-zrXu0zdTCsP

As a bonus, here's an endgame Trickster you could respec into later with better gear and more damage (relative to the mediocre Assassin gear; a well-geared Assassin will still do more than 2x the damage), but Trickster provides much better bossing and mapping sustain: https://pobb.in/2rHqZp8aW7tp

As a bonus bonus, here is the original Assassin build, but with moderately high budget gear (but all things considered not exorbitantly expensive) that can deal over 30M dps in burst scenarios: https://pobb.in/RRFCtjm68ekW

Edit: I've decided to be a bit more realistic and go for 2 hits on Helix instead of 3 and swap in Precision instead of Herald of Agony to lighten the need for Accuracy on rings. Gear is now actually rolled with res to show what to look out for. I've also decided to get all of our required Spell Suppression purely from the tree to ease up gearing for stats and res. Damage has dropped slightly, but is still overkill for a leaguestarter.

Edit 2: Do not use Devouring Diadem if you're also using a Doryani's Glorious Vanity. My covid-wracked brain made a mistake, my apologies.

Edit 3: According to another reddit user, Mistwalker's Elusive Effect is incompatible with Nightblade, and does not stack additively. In light of this, Ambush and Assassinate is the next best ascendancy for your Uber Lab.

This is not the case, Mistwalker does stack with Nightblade, and properly gives both the elusive effect and multi.