Here is the full list of all 21 Plants vs. Zombies GOTY Edition achievements. It takes around 40-50 hours to unlock all of the achievements on Windows.
Defeat 2 Gargantuars with Corn Cob missiles in a single level.
Discover the top secret zombie
Grow the Tree of Wisdom to 100 feet
Collect all 49 plants
Enable Mustache Mode
Get the golden sunflower trophy
Beat all 20 mini games.
Get 8000 sun during a single level.
Get to 20 flags in Survival Endless
Get to a streak of 10 in I, Zombie Endless
Get to a streak of 15 in Vasebreaker Endless
Bowl over 5 zombies with a single Wall-Nut.
Complete a daytime level by planting only Mushrooms and Coffee Beans.
Complete adventure mode
Defeat a normal roof level without using any catapult plants.
Blow up 10 zombies with a single cherry bomb
Complete a daytime pool level without using pea shooters of any kind.
Hypnotize the lead dancer zombie
Pick up 30 coins in a row on a single level without letting any disappear.
Complete a nighttime level without planting any Mushrooms.
Blow up a zombie using a potato mine