Like I said, Venti is COMPLETELY optional I don't even use him in the fight. I only use him to fill out 2 Anemo for the bonus. We use 2 Anemo and 2 Hydro. 2 Hydro will help you keep your HP topped off in case you take damage, and 2 Anemo will greatly assist you if you are forced into the fire pillar phase.
In this video, I beat Pyro Regisvine without taking any damage.
Unfortunately, Pyro Regisvine is FAR more difficult to beat easily if you do not own a Hydro unit. Barbara is the easiest and most Free to Play friendly option of the 3 Hydro units in the game as of Oct 10, 2020 because you CAN get her for free if you manage to hit Adventure Rank 20. This however is a bit late to get a Hydro unit. If you do not own a Hydro unit, you will have a hard time but this boss is NOT impossible.
NO HYDRO STRAT:
Use Kaeya's (or any Cryo unit) Elemental Skill to slowly whittle down the Core of the Pyro Regisvine to get it down. Then, DPS as hard as possible. Because you do not have any way to damage the head, you will need to wait around 30-40 seconds at least for the Pyro Regisvine's Core to regenerate to allow you to down it again.
ONE OF THESE MANDATORY UNITS:
Barbara
Mona
Xingqiu
Kaeya
Qiqi
Chongyun
IDEAL UNITS:
Venti (You can avoid the fire pillar segment with his Updraft)
Barbara
Mona
Xingqiu
MAYBE AVOID THESE UNITS FOR CORE DPS:
Xiangling
Amber
Klee (not released as of Oct 10, 2020)
Pyro Regisvine's only difficult segment is the fire pillars. This will take a lot of dashing to avoid entirely, but you can afford to tank 1-2 pillars if you need to. Aside from that, just focus on dealing damage to the core and the head, and you will easily clear this boss.
I beat my first Pyro Regisvine at AR27 World Level 2 on my first try. (I put in a lot of time outside of Liyue). In this video, I beat Pyro Regisvine using only Barbara without getting hit.
Let me know if you want more boss guides or even more in-depth boss guides for Genshin Impact
Youtube is removing tags so:
Pyro Regisvine, How to beat Pyro Regisvine, Pyro Regisvine Guide, Pyro Regisvine Genshin Impact, How to easily beat Pyro Regisvine, Pyro Regisvine No damage, Genshin Impact, Barbara, Barbara Genshin Impact, Mona, Mona Genshin Impact, Venti, Venti Genshin Impact, Free to Play, Genshin Impact Free to Play friendly, How to Beat Pyro Regisvine Free to Play, F2P, Venti, Amber, Xiangling, Pyro, Easy, Easily, Genshin Impact Guide, Genshin Impact F2P, Genshin Impact How to, Beginner, Expert, In Depth, Free to Play, Genshin Impact Free to Play