Plants vs. Zombies: Game of the Year

To Discover the top secret zombie you have to play through the game atleast once.
Then on your second run of the adventure mode you will encounter the zombie after 4-10.

Easiest way to achieve this was with this lineup atleast for me. Hope it helps other players

Very easy Achievement to get

Lanuch the game, Once on the main menu type "Mustache"

This achievement may be hard, but I've found an easier way to do it. It's almost the same method as money glitch except you keep retrying until you pass the wave. For that, open Vasebreaker Endless, pass the level but before more vases appear, exit to Main Menu so that the game can be saved. Then enter Vasebreaker Endless and continue. Complete the 2nd level and repeat the same process until you reach the 10th streak. You should easily unlock the achievement. But if you fail the level, do not click on "Try Again", otherwise you will have to start from scratch again as game will be automatically saved from where you started. Instead, exit to Main Menu and enter Vasebreaker Endless. You should see your saved game.