Mike Barnes is introduced in Cobra Kai Season 5, Episode 3 , titled “Playing With Fire.”

Quick note

He appears as Daniel and Chozen track him down, and that’s the episode where the character makes his first Cobra Kai appearance.

Show| Episode| Title
---|---|---
Cobra Kai| 5| 3
| | Playing With Fire 7

TL;DR: Season 5, Episode 3 — “Playing With Fire.”