Roy Alphard vs Velika: who would win?

Velika favored — Slight edge (~55%)

Roy Alphard · Re:Zero kara Hajimeru Isekai Seikatsu · Base

Tier

7-B, up to 7-A

Attack Potency

City Level, up to Mountain Level

Speed

Superhuman, up to Relativistic+

Durability

City Level+, up to Mountain Level

Velika · Bionicle · Base

Tier

7-B, up to 6-C

Attack Potency

City Level, up to Island Level

Speed

Massively Hypersonic+, up to Relativistic

Durability

City Level

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