Nightsider vs Giant-Killer: who would win?

Giant-Killer favored — Slight edge (~55%)

Nightsider · Warhammer 40,000 · Base

Tier

9-A

Attack Potency

Building Level+

Speed

Average Human, up to Speed Of Light

Durability

Human Level

Giant-Killer · Dungeons & Dragons · Base

Tier

9-A, up to 6-C

Attack Potency

Small Building Level+, up to Island Level+

Speed

Subsonic, up to Ftl+

Durability

Small Building Level+, up to Island Level+

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