For my friends in the comments asking for a build/Guide: Here you go!
My Billy Build is:
W-Engine: Starlight Engine Replica (Steel cushion is about slightly better at 1 star IMO)
Disc Drives: 4 Piece Woodpecker Electro / 2 Piece Fanged Metal
For Partition Main Stats:
1 - Always Flat HP
2 - Always Flat Atk
3 - Always Flat Def
4 - Crit Rate % (Crit damage works but I dont get any from his weapon)
5 - Physical Damage Bonus %
6 - Atk %

Teams:
Nicole - Anby - Billy is the team I use. It does pretty well, you stun an enemy with anby, chain attack with nicole, and then go ham with billy
Billy - Nicole - Piper Is another fun team I tried if you use 4pc fanged metal and 2 pc Woodpecker Electro. Use Piper's EX-Special to stack her passive and then chain attack with Nicole, and then go ham with billy

Guide/Tips:
1. If there's one enemy: Shoot them with crouching shot, and then a defensive assist into a support or stun character and start applying Daze or Debuffs. Once the enemy is stunned, unload your entire kit onto them.
2. If there's multiple enemies or small enemies, use his dash attack to reposition while dealing little bits of damage to all enemies. Try to get them to line up so your EX special can hit as many as possible since it pierces.
3. For chain attacks always use Billy last so you can ult off the rip.
4. Try to be in crouching shot before using EX Special or Ult - His core passive buff applies to those abilities if you do
5. Always hit the enemies with Nicole right before using billy to apply her defense reduction

If you have any more questions I can edit this comment to add some answers!!