Bloodletters vs Fomorian: who would win?

Fomorian favored — Slight edge (~55%)

Bloodletters · Warhammer 40,000 · Base

Tier

9-A, up to 1-A

Attack Potency

Large Building Level, up to Building Level+

Speed

Subsonic, up to Hypersonic

Durability

Small Building Level, up to Outerverse Level

Fomorian · Dungeons & Dragons · Base

Tier

9-A, up to 8-A

Attack Potency

Small Building Level+, up to Multi-City Block Level

Speed

Relativistic+, up to Ftl+

Durability

Small Building Level+, up to Multi-City Block Level

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