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