It seems you're asking about the "Diablo" tactic from Championship Manager 03/04 (CM 03/04), specifically looking for team instructions and how to apply that tactic in a 2021 context (likely meaning a modern replay, a modded database, or a retro tactic discussion from that year).
In CM 03/04 tactics screen (Tactics → Team Instructions): cm 03 04 diablo tactic team instructions 2021
The Diablo tactic for Championship Manager 03/04 is widely considered a "cheat" tactic that exploits a flaw in the game's match engine. It is typically built around a 4-1-3-2 formation, where a central midfielder makes late runs into the box that the AI defense fails to mark. Core Formation & Key Player It seems you're asking about the "Diablo" tactic