After watching about, pretty much every single Acheron build guide, pre release character run beta version, and general "what to expect" videos on yt, I think my consensus comes down to the most repeated points as well as a general overview eliminating all bias:
Lightcones: NO WAY of knowing how significant the DMG decrease is between an S5 Good Night Sleep Well light cone and her signature yet. Assume her best-in-slot is always her signature. What to do? Pull on the weapons banner till you get enough copies of GNSW to superimpose to the highest lvl unless you get her signature cone early.
Team comps: As a day 1 player, I have every standard 5* character and it's possible to run a sustain Welt team with Pela eventually Silver Wolf if I get her on rerun. However, some more options include:
- Acheron, Support Pela, Support Welt, Sustain Gallagher
- Acheron, Support Pela, Support Silver Wolf, Sustain Gallagher
- Acheron, Support Pela, Support Welt, Sustain Fire MC/Gepard with Trends of the Universal Market LC for extra debuff when hit
- Acheron, Support Pela, Support Sparkle, Any Sustain with TotUM LC (Sparkle cannot debuff so consider having a high speed (160+) Sparkle to make this work)
- Acheron, Support Kafka, Support Black Swan, Any Sustain
- ALL F2P: Acheron, Support Pela, Support Sampo, Sustain Natasha
Relics: Build her as a typical Hypercarry (CRIT DMG/CRIT RATE/ATK%/SPD) in order of stat prioritization) and make sure to have a Lightning DMG planar ornament
Traces: ULTIMATE UPTIME!!!! Make sure her Basic ATK and Ultimate trace lvls are as high as possible after unlocking the 3 major traces (bonus traces)
Overall: For supports, get as much speed and effect hit rate to apply as many debuffs as possible onto enemies to be able to achieve Acheron's Ultimate (her most powerful attack) as fast as possible and clear the enemy. THIS IS MOST IMPORTANT IF YOU'RE RUNNING A SUSTAIN WELT, BECAUSE HE CANNOT SUSTAIN INDEFINITELY (unlike Fu Xuan, or even as comfortably as Luocha or Huohuo)
Other Priories: If you don't have 2 invested 5* sustains, GET THEM FIRST because you don't want your Acheron dying on you during MOCs because you're too much of a gambling addict and didn't save up enough trailblazer power to properly farm the right relics (me)
Support character LC: With the lack of nihility LCs that provide debuffing benefits without having smtg to do w DOTs, main options include: Resolution Shines as Pearls of Sweat, Fermata (if one of your debuffers can apply a shock or wind shear), Good Night Sleep Well, and Before the Tutorial Mission Starts (free if you were a player during the first Silver Wolf banner). Kafka’s signature (Patience is all you need) is good as well, but if you’re using a 5 star lc it’s preferable to use smtg more accessible if you can’t get Acheron’s signature. Here’s a link to read up on their abilities
Her kit wants as many debuff applied to characters to get her ultimate out faster, though sometimes with a strong enough support harmony you may not even require a 2nd or 3rd nihility unit. Please be sure to check your own account’s character investment and calculate accordingly