Things You'll Need
Instructions
First, in order to play the Easter egg in Modern Warfare 2, you will need to beat the game by completing all levels. This can be done in any difficulty.
Make sure to NOT use any cheat codes while playing through the levels or the Easter egg may not be available.
Next, after beating each level go back into the Single Player menu of the game.
In the Single Player menu, go to Mission Selection. In Mission Selection you will see "Museum" at the bottom of the list (under Act III). Select and play the "Museum" level.
Once in the Museum, you will see that the halls of the Museum are populated with characters from all scenes of the game. The hidden Easter egg in Modern Warfare 2 is that you can make all of these characters come alive at once and attack you.
To do this, walk over to the museum desk in one of the halls. On the desk, you will see a button that says "Do Not Press". As you can guess, you must press this button to activate the Easter egg.
Finally, to complete the Easter egg you will need to kill all of the characters that come alive.