Stiyl Magnus vs Metal Bat: who would win?

Metal Bat favored — Slight edge (~55%)

Stiyl Magnus · Toaru Majutsu no Index · Base

Tier

7-A, up to 5-B

Attack Potency

Mountain Level, up to Planet Level

Speed

Sub-Relativistic

Durability

Small Building Level, up to Country Level

Metal Bat · One-Punch Man · Base

Tier

7-A, up to 5-C

Attack Potency

Mountain Level, up to Moon Level+

Speed

Massively Hypersonic, up to Ftl+

Durability

Small City Level, up to Moon Level+

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