Phaneroplus vs Alastor: who would win?

Phaneroplus favored — Slight edge (~55%)

Phaneroplus · Kaiju No. 8 · Honju

Tier
LOW 7-C
Attack Potency
Small Town Level
Speed
Subsonic
Durability
Small Town Level

Alastor · Hazbin Hotel · Base

Tier
LOW 7-C
Attack Potency
Small Town Level
Speed
Subsonic, up to Supersonic+
Durability
Building Level, up to City Block Level+

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