Mercenary
Gemling LegionnaireTwink Leveling Guide
Speed leveling league start guide
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My current character
Twister does the most unethical damage of all time it can be played on pretty much any ascendancy, here's a guide for how to do it on Gemling Legionnaire which in my opinion is easily the best version of the build, due to the unique quality effects Gemling gets via 
Advanced Thaumaturgy. Namely multiplicative attack speed for 
Whirling Slash, multiplicative projectile speed for Twister but most importantly "Chance to not remove Frenzy Charges" for 
Barrage can easily go up to 100% chance, therefore you permanently have max use Barrage which is extremely good for quality of life and damage. It's also extremely easy to stack quality, where-as spirit/spirit reservation stacking on an Abyssal Lich is not only extremely expensive, but the opportunity cost is significant, for less gain IMO.
Additionally there are inherent quality effects for the skills so you get to double dip on the value of stacking quality, and there's nice little damage buffs from our other skills such as our Heralds, 
Trinity, 
Charge Regulation etc.
On top of that Gemling has much better defense due to 
Virtuous Barrier effectively giving us 95% increased ES+Evasion for free, tons of life/mana regen, and we get crit immunity through 
Gem Studded
This version of the build has literally everything you want, and after personally trying it on 4 different ascendancies, I can confidently say if you want to best take advantage of this broken skill, you'll have a much better time on a Gemling, full stop.
If you wanted to play a different ascendancy, the next best option is 
Deadeye due to very good frenzy charge generation with 
Called Shots + 
Sniper's Mark, 
Avidity, extra damage via 
Thrilling Chase, and getting Tailwind for free for Skill Speed, Evasion, and Deflect value. You also start at the correct side of the tree saving you an entire Jewel socket. It's honestly pretty neck and neck with gemling, it's just way easier to get proj speed on gemling. After that I'd go Abyssal Lich, since you get a lot of projectile speed scaling via 
Umbral Well. However i'm personally not a huge fan of this setup as the opportunity cost involved for getting spirit everywhere + spirit reservation is very high + costly. On top of that the rest of the Ascendancy doesn't provide much, you get some ES and an extra jewel socket which is pretty nice if you have a giga jewel in there. Beyond that though, you have very weak frenzy charge generation so you're pigeon holed into going Armour Break III + 
Resonance for frenzies, which leaves you with no way to generate frenzies if you are on a boss. This also means if you don't have a pure phys spear, and over-damage the content, your frenzy generation won't be great. Of course there's Spiritwalker which gets a lot of extra projectile speed and projectiles via 
Primal Bounty. It's very strong early game, but once you start scaling a lot of speed it feels awful to play around since you have to dodge every 3 casts and time everything correctly otherwise you just get 0 value. IMO it's a cumbersome playstyle and insanely un-fun. It also is just objectively slower, and when I derive 90% of my fun from being extremely fast & efficient, I would simply never play this ascendancy for twister ever again, and would likely pick almost anything else over it. 
Oracle I've seen do some shenanigans with crit scaling + path unforseen. 
Witchhunter could unironically be pretty decent with an extra 100 weapon set points just to go insanely fast, and 
Sorcery Ward is very good defensively.
