Kamen Rider Decade vs Ghast: who would win?

Kamen Rider Decade favored — Slight edge (~55%)

Kamen Rider Decade · Kamen Rider · The 9 Rider Worlds Arc

Tier

9-B, up to 2-A

Attack Potency

Wall Level, up to Multiverse Level+

Speed

Massively Hypersonic+, up to Ftl

Durability

Wall Level, up to City Level

Ghast · Minecraft · Base

Tier

9-B, up to 8-C

Attack Potency

Wall Level, up to Building Level

Speed

Average Human, up to Subsonic

Durability

Small Building Level

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