Yae Miko, A.K.A. "the better Fischl", (that is a joke) is an excellent five-star electro catalyst wielding on-field and off-field damage dealer. She is often overlooked and undervalued because of people's tendency to compare Yae with the four-star Fischl. Although some believe Yae Miko is not worth the primogems because of Fischl's free-to-play friendly aspect which is a valid opinion, I believe Yae Miko is still a great pull for her versatility, great AOE and single-target damage and electro application, and ease of build.
Why should/shouldn't you build Yae Miko?
Even if you already own a built c6 Fischl, Yae Miko is still not a bad pull! In fact, it might be a very good upgrade for your account because Yae Miko and Fischl synergizes well.
Both Fischl and Yae Miko's kit are perfect for this team. Yae Miko becomes a great Fischl driver by consistently being able to proc Fischl's A4 passive even off-field! Also, Yae's (sort of) hybrid damage scaling of attack and elemental mastery works wonderfully for aggravate. With Kazuha's viridescent venerer shred, elemental damage bonus buff, and Nahida's elemental mastery buff, both Yae Miko and Fischl will deal a great deal of damage. Not to mention the entire team's energy requirement significantly lowers. Fischl and Yae Miko generate particles every second with practically 100% uptime. Additionally, the electro resonance will supply even more particles.
Also, compared to Fischl, I would argue that Yae Miko is generally better as an off-field damage dealer. Yae Miko deals higher raw damage, has longer skill duration, does not rely on burst, does better against multiple opponents, has bigger skill range, and does not rely on elemental reactions (not consistently procing Fischl's A4 is a huge damage loss).
There are specific cases though which makes Fischl better than Yae Miko as an off-field damage dealer. In particular, Fischl (especially at c6) is a better teammate for Clorinde or Sethos in aggravate teams, Fischl is better than Yae in taser teams (especially those that include swirl damage dealers such as sucrose or kazuha), and Fischl has more particle generation. Note though that Yae Miko still performs well in these areas! Fischl is just a bit better.
Best artifacts
This set is perfect for quicken, quickbloom, and hyperbloom teams where Yae Miko greatly benefits from both the elemental mastery buff and attack buff.
Yae Miko's best weapons
Kagura's Verity is unquestionably her best weapon.
Best teammates for Yae Miko
Yae Miko's team compositions
This team deals a lot of damage! Probably the most! The combination of Yae and Furina's skill damage, hyperblooms, and aggravate plunges sums to extremely high team DPS. The catch is each member needs quite a bit of energy recharge, so you'll have to invest in that!
Xianyun holds the Viridescent Venerer set to shred electro and hydro resistance and more importantly, allows Yae to plunge. This not only benefits Yae's personal damage, but Xianyun also makes triggering hyperblooms easier with Yae's plunges. Additionally, Xianyun is a teamwide healer, which allows us to run Furina without reserving another spot for a healer.
Nahida is the best support for every team that features dendro-related reactions. Nahida will greatly buff the team's reaction damage, which this team has lots.
Furina is the perfect final slot. Furina provides high personal damage, strong damage buffs, and good off-field hydro application which allows for the occassional blooms.
Yae Miko Techs
Yae Miko's charge attack does not have ICD. This is important especially in aggravate teams with Fischl. When on field, the player should charge attack with Yae Miko, and because her charge attacks does not have ICD, so long as the opponents are affected by quicken, Yae will always aggravate. Yae can be a Fischl driver this way. The problem is Yae's charge attack animation takes painfully long to end. Yae Miko can quickly dish out charge attacks by performing jump cancels to skip Yae's long animations.