Combustion Man vs Zapper: who would win?

Zapper favored — Slight edge (~55%)

Combustion Man · Avatar: The Last Airbender · Base

Tier

8-A, up to 7-C

Attack Potency

Multi-City Block Level, up to Town Level

Speed

Massively Hypersonic+

Durability

Multi-City Block Level, up to Town Level

Zapper · Undertale · Base

Tier

8-A

Attack Potency

Multi-City Block Level

Speed

Speed Of Light, up to Ftl

Durability

Multi-City Block Level

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