Valeriy
Valeriyis a 4 star Electro Support, made to be used primarily in Electro Stellar-Conduct teams with some limited viability in other Electro teams. As a 4 star with an Electro Vision and no Stellar Linchpin, Valeriy will not inherently enable the Stellar-Conduct Reaction in his teams.
Valeriy's Skill provides an Electro Shield to the team, while his Elemental Burst will deal some off-field Electro DMG and periodically apply Electro. Due to this and how his buffs work, Valeriy's main niche is found in on-field 
Mitya teams and little else.
After using his Skill or Burst, Valeriy will gain a special resource called Impact Momentum. When he has enough Impact Momentum, he can consume it to cast a special Charged Attack, and after using it, he will provide quill-like effects to teammates' Electro DMG. Consuming more Impact Momentum than required will further increase this effect, based on the amount consumed, with this increase being tripled for Electro Stellar-Conduct DMG compared to other sources of Electro DMG.
As a 4 star character, further buffing and enhancements to his kit will be found in his Constellations and especially his C6, which contains the majority of his buffing.
- At C0, Valeriy will only provide quills.
- At C2, he will provide a teamwid 100 EM Buff.
- At C6, he will give 10% Crit Rate to all Electro DMG and an additional 40% Crit DMG to Electro Stellar-Conduct DMG only.
Valeriy only becomes a worthwhile option with his Constellation 6, being entirely subpar without it even for Mitya teams. He will be featured on Mitya's banner, but as a newly released 4 star, acquiring his C6 without also getting some Mitya Constellations along the way will be a tall task.
Besides on-field Mitya, he will likely be decent for 
Cyno but probably not better than other options. He will not a better option than a unit like 
Sucrose in a 
Flins team or even 
Iansan in an Electro 
Varka team. He should be considered a Mitya exclusive support.
Mitya
Vodyanitsa
Vesna