Keys were also originally in the international version of Plants vs. Zombies 2: It's About Time, but were removed in the 1.7 update, as a new method of unlocking plants and rewards replaced the original layout. Any keys the player had before the update were turned into coins. World progression now takes place through the use of World Keys obtained by defeating the Gargantuar level for the first time in any world.
How to obtain
Keys are found as a rare drop off of all zombies killed in a time zone. The odds of a zombie dropping a key are relatively low, around one percent off of any zombie, regardless of health or speed. Keys could also be found off of the Treasure Yeti every once in a while, and a lunchbox can carry three keys of the area the Yeti was killed in. Finally, Piñata Party piñatas had a chance to carry one key for any area, as long as they player had that area unlocked.
Killing the Treasure Yeti was one of the best ways to get keys, as every other lunchbox has three keys.
Playing levels with a high zombie density provided more chances for keys to drop.
Completing Piñata Parties could have resulted in a few keys being rewarded.
Zombie strength does not effect drop chances, so it was more practical to battle large amounts of weaker zombies for key farming.
Plants vs. Zombies 2: It's About Time
This section is about something that is China exclusive.