The Item Of The Month (IOTM) was implemented into the game on 2nd of March 2017.
Every month, a limited item is made available in the Growtopia Store, where it can be bought for a certain amount of Gems. The Item Of The Month of March, April, May, and June of 2017 all cost 100,000 Gems. Since July 2017, the price for the IOTM rose to 200,000 Gems to increase their value. During January 2021, the price for IOTM rose to 350,000 Gems to keep the item's value when then they are no longer in the store.
The item is only available in the store for one month, and once it is taken out of the store, it can never be obtained again.
The IOTMs can be seen on the Growtopia Forums.