Mutant Rat vs Rudeus Greyrat: who would win?

Mutant Rat favored — Slight edge (~55%)

Mutant Rat · Godzilla · Base

Tier

6-C

Attack Potency

Island Level

Speed

Subsonic, up to Supersonic+

Durability

Island Level

Rudeus Greyrat · Mushoku Tensei ～Isekai Ittara Honki Dasu～ · Base

Tier

6-C

Attack Potency

Island Level

Speed

Superhuman

Durability

Wall Level

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