Coily Rattler vs Flame Reaver: who would win?

Flame Reaver favored — Favored (~65%)

Coily Rattler · Kirby · Base

Tier

4-A

Attack Potency

Multi-Solar System Level

Speed

Massively Ftl+

Durability

Multi-Solar System Level, up to Low Multiverse Level

Flame Reaver · Honkai: Star Rail · Base

Tier

3-C, up to 2-A

Attack Potency

Galaxy Level, up to Multiverse Level+

Speed

Ftl+, up to Infinite

Durability

Galaxy Level, up to Multiverse Level+

A heuristic estimate from normalized VS Battles Wiki stats: tier, attack potency, speed and durability.