Giant Space Amoeba vs Isshiki Ōtsutsuki: who would win?

Giant Space Amoeba favored — Slight edge (~55%)

Giant Space Amoeba · Star Trek · Base

Tier

4-B, up to 3-C

Attack Potency

Solar System Level, up to Galaxy Level

Speed

Massively Ftl

Durability

Solar System Level

Isshiki Ōtsutsuki · Naruto · True Form

Tier

4-B

Attack Potency

Solar System Level

Speed

Ftl, up to Massively Ftl

Durability

Solar System Level

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