From Dragon Mania Legends Wiki
Introduced in Update 4.8, Piggy Bank Events are limited-time events in which Trainers reach individual milestones and collect rewards through spending Gems on any feature in the game. Each one Gem spent is equal to one Gem added to the bank, regardless of what it was spent on. Leveling up earns 20 Gems and completing a collection earns 50 Gems. Gems are not automatically added to the Trainers Gems bar, they must be manually collected from the bank. A minimum of 300 Gems must be earned before the bank can be broken to retrieve any Gems. A maximum of 600 Gems can be earned throughout the event. The event banner will display 'FULL!' upon reaching the maximum capacity. Trainers must pay real currency, in the amount of $3.99 USD, to break the bank. Once the bank has been broken and the Gems collected, the event will disappear, regardless of whether the time limit has expired. Any Gems not collected before the end of the event will be lost. These events start at ??:00 UTC and end at ??:00 UTC.