Fomorian vs The Morrigan: who would win?

Fomorian favored — Slight edge (~55%)

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

The Morrigan · Assassin's Creed · Base

Tier

9-A, up to HIGH 8-C

Attack Potency

Small Building Level+, up to Large Building Level

Speed

Superhuman, up to Supersonic

Durability

Large Building Level

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