Medal is a currency item exclusive to the Chinese version of Plants vs. Zombies 2. They can be obtained by playing PvP Mode, either by defeating other players, or wait to automatically generate Metal. Medals are used to purchase Puzzle Pieces.
Originally, medal was a currency item that could be obtained by completing levels in the Endless Zone events, and at times was dropped by zombies. As the player progressed through the levels, their rewards of this currency increased. Medals were used to unlock plants that require Puzzle Pieces to be unlocked. They could also be used to purchase Puzzle Pieces themselves.
Since April 3, 2015 and until PvP Mode's release, medals could not be obtained, as their supporting event was no longer available.
They are currently used as a currency in PvP Mode for the same purposes