Bowser's Brother vs Zwei (RWBY): who would win?

Bowser's Brother favored — Slight edge (~55%)

Bowser's Brother · Super Mario Bros · Base

Tier

8-C, up to 5-C

Attack Potency

Building Level, up to Moon Level

Speed

Massively Ftl+

Durability

Building Level, up to Moon Level

Zwei (RWBY) · RWBY · Base

Tier

8-C

Attack Potency

Building Level

Speed

Hypersonic

Durability

Large Building Level

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