Korra vs Karsus: who would win?

Karsus favored — Slight edge (~55%)

Korra · Avatar: The Last Airbender · Cosmic Korra

Tier

5-C

Attack Potency

Building Level, up to Moon Level

Speed

Sub-Relativistic

Durability

Moon Level

Karsus · Dungeons & Dragons · Archwizard of Netheril

Tier

HIGH 6-A, up to 2-A

Attack Potency

Multi-Continent Level, up to Multiverse Level+

Speed

Relativistic+, up to Infinite

Durability

Multi-Continent Level, up to Multiverse Level+

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