Mata Nui vs Ultima Weapon: who would win?

Ultima Weapon favored — Slight edge (~55%)

Mata Nui · Bionicle · Great Spirit Robot

Tier

HIGH 5-A, up to 4-B

Attack Potency

Brown Dwarf Level, up to Solar System Level

Speed

Sub-Relativistic+, up to Nigh-Omnipresent

Durability

Brown Dwarf Level, up to Star Level

Ultima Weapon · Final Fantasy · Base

Tier

HIGH 5-A

Attack Potency

Brown Dwarf Level

Speed

Massively Ftl

Durability

Brown Dwarf Level

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