both...? its why you have multiple tabs for each character and weapon.

she mostly relies on her 4th skill which is based on her HP
so basically give her 2 hp modules then the rest on skill duration and skill cool down
I think mine got like 40k hp and able to one shot the whole rooms in vep30

I recently came back myself. Of all the content creators OrneryBiscuit hands down makes the best build guides. In-depth, math done, testing, etc.

https://www.youtube.com/@OrneryBiscuit

This is what I usually run, you can use it both for mobbing and bossing:

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3518824156

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3518824564

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3518824809

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3518826354

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3518833605

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3518826129

If you care to bother hitting weakpoints then using last dagger is better.

Serena is literally an all arounder. She's good at pretty much at everything, bossing, mobbing, dungeons.

She's not on Ines, Bunny, or Freyna level when it comes to mobbing and dungeons though but still really good.

When it comes to bossing I say she's better than Gley and Hailey.

Her main weapon is most likely the Ancient Knight, she's has other weapons that are good too. Like Last Dagger, Smithereens, Restore Relic, A-TAMS, Malevolent.