エウルア

Songs of Broken Pines:
This weapon has the highest base ATK of any weapon in the game, combined with a substat that gives Physical DMG bonus, passive that gives the entire team ATK speed and additional ATK%, makes it her BIS

ATK% substat weapons:
Wolf's Gravestone, Beacon of the Reed Sea, Luxurious Sea-lord, Protype Archaic, Akuoumaru
Since Eula's damage does not rely on reactions, having higher ATK stats/buffs greatly increase her damage. Wolf's Gravestone's passive and naturally high ATK stat as a 5* weapon makes it comparable to her signature weapon. This is similar for Beacon of the Reed Sea, which gives CRIT Rate and ATK%. Luxurious Sealord and Akuaoumaru are a great options, boosting her Elemental Burst damage alongside their ATK% substat.
Other options:
Serpent Spine
A battle pass weapon with a CRIT rate substat and a powerful passive skill that lets it sometimes rival 5* weapons, due to it's low base ATK, ATK% buffs scale very well.
Snow-tombed Starsilver
An alternative option if you don't have billets or don't want to craft Prototype Archaic, since it is completely free. It has a high base ATK stat + Physical DMG bonus, and it's passive is especially useful when Rosaria is on the team

<sands> ATK% or Energy Recharge
<goblet> Physical DMG Bonus
<circlet> CRIT Rate / CRIT DMG

Energy Recharge
CRIT Rate
CRIT DMG
ATK%

1) Elemental Burst: Glacial Illumination
2) Normal Attack: Favonius Bladework - Edel
3) Elemental Skill: Icetide Vortex

It is highly recommended to use [Genshin Optimizer](https://frzyc.github.io/genshin-optimizer/#/), when deciding to prioritizing between CRIT DMG and ATK%, since the performance of these two stats may change depending on your weapon, teammates and the presence of external ATK% buffs