Dehya, Mantichora, Flame Mane, leader of the Eremites, overthrew Hu Tao and has the highest base hp in the game. This is tacit acknowledgement towards Hu Tao's crimes and corruption.
Her E creates a 10m radius field that does a coordinated aoe pyro attack upon hit. It can proc once every 2.5s, so it can melt/vape each hit. The E dmg has dual atk + hp scaling. This means she will be buffed by both pyro resonance (atk buffs) and hydro resonance (hp buffs).
Dehya can reposition the field once during its duration. It has a 20s cd and 12s duration (which can increase to 18s with c2). Her E can snapshot. The initial hit and reposition both apply 1A pyro.
With her Q Dehya goes into boxing mode and gains infinite poise (like Raiden Q). By default it can do 6 punches and one final kick, all of which have decent aoe. During this 4s quicktime event, if the NA/E buttons are pressed in rhythm, Dehya can do up to 10 punches and one final kick.
With her passives, the field gives poise and damage reduction. Dehya can mitigate damage taken by characters within the field. Moreover, she can heal herself.
C1 gives more hp scaling on E and Q as well as +20% hp. C2 extends duration of E by 6s to 18s. It also gives 50% dmg bonus on E when characters are attacked. C4 makes Dehya restore energy and hp during Q. C6 extends Q duration by 2s to 6s. It also gives CR/CD buff.
4p crimson, 4p tenacity, 4p gilded, 4p marechausse, 4p vourukasha, 4p golden troupe, 4p emblem, 2p glad/VH, and mixed sets are fine
Can use atk or hp sands. Substats include crit, ER, atk, hp, even EM (for burgeon teams).
Redhorn fits Dehya's flamemane aesthetic better than reed beacon. WGS, Skyward Pride, Serpent Spine, Fish claymore also work well.
Dehya can be placed on almost any team in the game. Examples include Childe international, Scaramouche teams, burgeon teams, Rational teams, melt/vape teams, even Xiao and Itto teams.
Dehya can be used as a replacement for Thoma in Hu Tao teams: e.g. Dehya-Kazuha-Yelan-Hu Tao (as Dehya provides pyro app for vv to swirl). Dehya can also be used in freeze-melt teams such as: Dehya-Bennett-Ayato-Ganyu.
Dehya can support Lyney teams by generating pyro particles, applying pyro, and reducing dmg (given that Lyney sacrifices hp and can be squishy).
She can be played in Noctis curry teams (to give stack and poise resistance). She can be played in Wrio melt or fridge teams (with say Dehya-Nahida-Wrio). She can also be paired with Focalors for hp manipulation and vapes.
Assume 2k atk and 30k hp (achievable even with atk sands given Dehya's high base hp). With Bennett, she can reach 3k atk. So hp is 10 times the atk. Assume lv10 E and Q.
Her E has 108.36% ATK + 1.86% HP scaling. The hp part is equivalent to 18.6% atk scaling (multiply by 10), so the effective scaling is 126.96% per hit.
When she casts her E she does 203.18% scaling. When she repositions her E she does 239.04% scaling. These hits have independent ICD (both can melt/vape). One can cast her E and immediately afterwards reposition her E to get both hits in at the beginning.
During the 12s duration of the field, her E can proc 4 times. The total scaling is $$203.18 + 239.04 + 4*126.96 = 950.06$$
Assume Dehya has 61.6% pyro dmg bonus (e.g. via 2p crimson). Assume all of the E hits melt (multiply scaling by 2). Given the 20s cd of the E, the dps is $$x_E = 2*950.06*1.616/20 = 153.5$$
Now consider her burst damage. Her Q has 177.66% ATK + 3.05% HP scaling per punch and 250.74% ATK + 4.3% HP scaling on the final kick. This is equivalent to 208.16% scaling per punch and 293.74 scaling on the kick.
Suppose she does 10 punches. The total scaling is $$208.16*10 + 293.74 = 2375.34$$ which is quite high. Some of these punches/kicks can even melt/vape.
Given the 18s cd of her Q, the dps is $$x_Q = 2375.34*1.616/18 = 213.25$$ which is higher than the E dps interestingly. This suggests some builds where the burst is prioritized over the E sub-dps.
Using the 3 hit rule, and assuming kick and punches have independent icd, suppose 4 punches melt, and the final kick melts. The scaling is then $$208.16*14 + 293.74*2 = 3501.72$$ which increases Q dps by 1.5 times. The mv is then $$x_Q = 3501.72*1.616/18 = 314.4$$
The total dps is then $$x_E + x_Q = 467.9$$ This is Raiden/Yae level, which is pretty good, given that Dehya seems to be designed with supporting features.
One can increase the burst dps using 2p noblesse, Raiden E, 4p emblem, certain anemo abilities, but most importantly Mona's Q. Dehya's Q last 4s, so Mona's omen buff can apply during the whole duration (one can also use Focalors' buff). Suppose Mona's Q gives 60% dmg bonus. Then Dehya's Q dps is $$x_Q = 3501.72*(1.616+.6)/18 = 431.1$$ The total dps is then $$x_E + x_Q = 584.6$$ which is higher than C1 Hu Tao.
By using 4p emblem, the dps can increase even more. Suppose Dehya has 200% ER and 4p emblem for 50% dmg bonus on Q. The E dps is then $$x_E = 2*950.06*1.466/20 = 139.28$$ and the Q dps is $$x_Q = 3501.72*(1.616+.6+.5)/18 = 528.37$$ The total dps is then $$x_E + x_Q = 667.66$$ which is actually top tier.
C1 gives 3.6% hp scaling on E and 6% hp scaling on Q. This is equivalent to 36% and 60% scaling. Her E hits 6 times, and her Q hits 11 times (with 5 melts). The dps is $$x_E = 2*(950.06+6*36)*1.466/20 = 170.9$$ and $$x_Q = (3501.72+16*60)*(1.616+.6+.5)/18 = 673.2$$ The total dps is then $$x_E + x_Q = 844.1$$
C2 extends E duration by 6s and can give 50% dmg bonus per hit on E. This allows for 3 more hits for a total of 7 coordinated E attacks within 18s. The E dps is $$x_E = 2*((203.18 + 239.04 + 2*36)*1.466 + 7*(126.96+36)*1.966)/20 = 299.65$$ This is actually a significant increase in E damage (~1.5 more damage, which is very good). The total dps is then $$x_E + x_Q = 972.85$$
She gets increased scaling on E and Q. Assume lv13 values. The dps is $$x_E = 2*((239.87 + 282.2 + 2*36)*1.466 + 7*(127.93+21.9+36)*1.966)/20 = 342.8$$ and $$x_Q = ((209.74+36+60)*14+(296.01+50.7+60)*2)*(1.616+.6+.5)/18 = 768.59$$ The total dps is then $$x_E + x_Q = 1111.39$$
Her Q is extended to 6s. Suppose she can now do 5 more punches for a total of 15 punches (5 melts). The Q dps is $$x_Q = ((209.74+36+60)*20+(296.01+50.7+60)*2)*(1.616+.6+.5)/18 = 1045.39$$ which is a significant buff to the Q. This is not even considering the cr/cd buffs from the c6. The total dps is then $$x_E + x_Q = 1388.19$$ which is also top tier among C6 characters. Her C6 essentially doubles her C0 damage, and almost all of Dehya's constellations provide significant buffs to her damage. Other characters whose C6 can double (or triple) their C0 dps include Cyno, Itto, and Xiao.