Preondactyl vs Alastor: who would win?

Preondactyl favored — Slight edge (~55%)

Preondactyl · Kaiju No. 8 · Base

Tier
LOW 7-C, up to 7-A
Attack Potency
Small Town Level, up to Mountain Level+
Speed
Superhuman, up to Hypersonic
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.