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