The Great Holy Spirit vs Simon the Digger: who would win?

Simon the Digger favored — Slight edge (~55%)

The Great Holy Spirit · Tensei Shitara Slime Datta Ken · Base

Tier

1-C

Attack Potency

Complex Multiverse Level

Speed

Omnipresent

Durability

Complex Multiverse Level

Simon the Digger · Tengen Toppa Gurren Lagann · Post-Multiverse Labyrinth

Tier

HIGH 1-C

Attack Potency

High Complex Multiverse Level

Speed

Subsonic, up to Immeasurable

Durability

High Complex Multiverse Level

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