Kakran Grandmother vs Obsidian: who would win?

Obsidian favored — Slight edge (~55%)

Kakran Grandmother · Star Wars · Base

Tier

HIGH 6-A, up to 5-C

Attack Potency

Multi-Continent Level, up to Moon Level

Speed

Massively Hypersonic, up to Massively Hypersonic+

Durability

Multi-Continent Level, up to Moon Level

Obsidian · Steven Universe · Steven Fusion

Tier

HIGH 6-A

Attack Potency

Multi-Continent Level

Speed

Relativistic

Durability

Multi-Continent Level

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