You can do this by yourself, with just 1 controller total (no extras needed).
• Select
Multiplayer from the main menu.
• Select
Custom Multiplayer.
• Select
Halo 2.
• Select
Halo 2: Anniversary (
do not select Classic).
• This works on ANY "H2A" level!!! It will default on Lockdown. Press

.
You need to CHOOSE GAME TYPE:
• Press down

and right

, to select JUGGERNAUT. Press

and

again.
• The Options don't matter, so press

, and

to Start.
• • Walk around for 30 seconds for the requirements to be met. Mine popped around 35-40 seconds in-game.