World Key

World Keys were added in the 1.7 update of Plants vs. Zombies 2: It's About Time. These were added to replace the stars, so one world key is needed to get to the other world. The player can get one after beating the level 8 of each world (level 10 in Dark Ages), in which the last Gargantuar of the respective world is killed.

Usage
It can be used to unlock any world, as the description says when the Player gets it. Therefore, the Player can go to any world in any order.

Trivia

 * The statue present in each area in level 8 has a Gargantuar of the respective world holding a World Key in its hand.
 * The Gargantuar level in Dark Ages is on level 10 instead of 8. This does not change the game in any way other than having to progress through 2 more levels.