Mega Man (Megamix/Gigamix) vs Kamen Rider Dark Kabuto: who would win?

Kamen Rider Dark Kabuto favored — Slight edge (~55%)

Mega Man (Megamix/Gigamix) · Mega Man · Base

Tier

5-C, up to 5-B

Attack Potency

Moon Level+, up to Planet Level

Speed

Subsonic, up to Massively Ftl

Durability

Moon Level+, up to Planet Level

Kamen Rider Dark Kabuto · Kamen Rider · Kamen Rider Dark Kabuto

Tier

LOW 5-B

Attack Potency

Small Planet Level

Speed

Superhuman, up to Ftl

Durability

Small Planet Level

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