Alastor vs Stagshroom: who would win?

Stagshroom favored — Slight edge (~55%)

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+

Stagshroom · Godzilla · Base

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

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