Fischl is unquestionably one of the best characters in Genshin Impact. You won't necessarily use her for her skill with the bow but more for its summoning of Oz: a crow that persists even after character switching and will greatly facilitate elemental reactions. She also has a passive that will reduce the duration of expeditions in Mondstadt by 25%, which is not negligible.
Recommended weapons
Skyward Harp
5 Star Bow
Base ATK 48
Obtaining Wishes
Increases critical damage by 20%. Hitting an enemy has a 60% chance to inflict physical damage equal to 125% of attack in a restricted area. This effect can be triggered once every 4 seconds.
The Stringless
4 Star Bow
Base ATK 42
Getting Wishes
Increases damage dealt by Elemental Skills and Elemental Bursts by 24%
Artifacts
Thundering Fury
2 pieces equipped : Electro damage bonus + 15%
4 Piece Teams : Increases damage taken from Overload, Shock, and Overconduction by 40%. When you trigger these elemental reactions, the elemental skill TOR is reduced by 1s. This effect can be triggered once every 0.8 seconds.
Bloodstained Chivalry
2 pieces equipped : Increases physical damage by 25%.
4 pieces equipped : Using charged attacks does not consume stamina for 10 seconds after an enemy is defeated, and damage dealt is also increased by 50%.
Fischl's first constellation point is crucial because it further optimizes his offensive capacity. With this, your enemies will take extra damage from your pet with each of your attacks. In addition, this damage will be of the Electro element, a plus if your target is weak against it.
To play alongside:
Tartaglia
With Fischl, you will want to electrocute as many targets as possible. Tartaglia is one of the best characters to apply Hydro effects in order to then trigger chain electrocutions with your archer!
Qiqi
The superconducting effect is too often underestimated. With Qiqi and Fischl, you will be able to trigger this effect almost permanently, thus reducing enemy physical damage.
If you're looking to power-up your Hu Tao here is our complete guide from artifacts to weapons.