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