[2.4] Assassin Frost Bomb Trapper

Intuitive LeapCheap Construction

So Frost Bomb, normally a support skill, is the weapon of choice for this build. Normally limited by a 2.5 second casting cooldown (with some helm enchants to cut up to 30% off), that's way too slow for an actual build. Enter the Trap Support, which overrides the cooldown of this skill with the cooldown of the trap, which then gets lowered by passives and the Trap Cooldown Support gem for 66%+ reduced cooldown. Frost Bomb normally has a 3.5 second cooldown, but by running a quality Less Duration we can cut that down to about 1.4 seconds, which is admittedly janky but still workable. Damage supports of choice are Added Cold Damage and Trap and Mine Damage (in order of effectiveness). So our final links are Frost Bomb/Trap/Trap Cooldown/Less Duration/Added Cold Damage/Trap and Mine Damage.

Other link set ups are Bear Trap (from Jaws of Agony)/Crit Chance/Added Fire/Power Charge on Crit to help with charge generation and single-target while waiting for Frost Bomb traps to recharge; Flame Dash/Faster Casting for movement (because we get no attack speed for Whirling Blades); Temporal Chains/Blasphemy/Arctic Armour/Enlighten(lv2) (although the Enlighten isn't strictly necessary, just nice); CwDT/Immortal Call/Increased Duration/Vaal Lightning Trap; Clarity. The build has about 4 free sockets that I haven't decided what to fill with yet.

I went Assassin over Saboteur (going the two Power Charge nodes, then the Crit on Full life node), mainly since I'm focusing on large, freezing, hits, rather than smaller ones provided by Cluster Trap/Chain Reaction combinations, as well as the potential for a more effective Uber Lab point allocation (Culling Critical Strikes compared to grabbing blind chance on Saboteur) if I ever do Uber Lab.

The passive tree focuses on life, with a lot of nearby damage clusters allocated (Blast Cascade, Throatseeker, Doom Cast, Power Charges etc. are all more or less on the way to life nodes). The outlier in the order is the Scion Life wheel, which is just too good to pass up. Significantly, Clever Construction (traps can't be damaged 5 seconds after being thrown) is not allocated, but I found that only a few mobs in the game really threaten traps reliably (Frost Orb Elementals, Arcwitches, Piety/Storm Heralds) and these don't spawn in large packs, so with a bit of kiting you can get by. If I had another ~7 levels to spare though, I'd be tossing up between grabbing it for deal with those edge cases (and for the neato High Explosives in the same wheel) or going dual curse and ditching Arctic Armour.

Uniques for the build are Sunblast and one Cheap Construction, which combined with the 10% reduced duration on Less Duration's quality bonus, gives us near-instantly detonating traps. Jaws of Agony gives us a single-target set up in Bear Trap and helps with Power Charge generation. Less required but still strong uniques include http://pathofexile.gamepedia.com/Facebreaker for the obvious crit multi, Divinarius and Carcass Jack for the AoE and damage Rumi's Concoction) as a strong defensive flask choice, and Intuitive Leap to save 4 points in the Shadow cluster on the right side of the tree.

Other options for gear are plentiful.

Any pair of crit gloves should work, but you can drop them for resistance gloves on Elemental Weakness maps (at 146/163/146 in HO right now) if you don't have better gear than I do.

Golems aren't run to prevent enemies dropping below full life before they get hit, but either Stone, Flame or Chaos Golem would work.

Cold Penetration works as a gem link, but because we already gain resistance reduction from Frost Bomb itself, is less effective as a multiplier than it otherwise would be so Trap and Mine damage is better in the general case, but I haven't done exact math so I might be a little off there.

Warped Timepiece lowers duration of Frost Bomb and I used it myself until the low 70s, but because Less Duration makes it 50% as worthwhile due to stacking multiplicatively rather than additively, I switched to a solid rare piece with life on it instead.

The final and probably biggest build choice is to go Hrimburn and Rapid Decay, Rapid Decay lowers the cooldown by 15% and Hrimburn allows Rapid Decay's DoT multiplier to be worthwhile, but I originally ran this set up for a while and didn't feel much change when I dropped Rapid Decay jank-wise, but the damage of an extra support and Facebreakers did feel better to me. That said Maceless (link below) posted a thread the same day I started this build up myself and he said he did this combo (with a different passive tree with Elemental Equilibrium allocated) so there's definitely potential here, I just feel the version without this combo is better overall, even if the single-target potential may be a bit lower admittedly (although I haven't mathed that all out and whether or not you run Trap Cooldown for pack clear or swap it out maybe for bosses changes the results).

Arctic Armour can be swapped for Herald of Ice if you want, but I felt that even with all the running around this build does, it has enough damage and not enough defense. If you get an amazing amulet or level half a dozen more times, you can go Dual Curse and stick in Elemental Weakness or Enfeeble over either of those previous options instead.

Lastly, CI should be a solid option for this build too, I just felt with Jaws of Agony and Carcass Jack both giving life, and almost all the life nodes being right next to the damage clusters I wanted on the tree life would be a much easier option, but if you went for Orb of Storms/PCoC, ditched Jaws of Agony and Carcass Jack, slotted in Increased Area of Effect over Trap and Mine Damage (swapping for Conc. Effect on bosses) and swapped Arctic Armour for Discipline with a better Enlighten and that one 4% reduced reservation node next to CI you'd still have a solid build, that'd probably be better with more investment (as ES always is).