*Purchase 100 energizers.
Energizers are basically potions that refill your action meter. You will get them in the game through various ways (collections, quests, reward huts). You don't have to buy them, though the option is there. Even better is that you will be rewarded with the currency to buy them in game, so you don't have to waste any actual money to get them.
Just having the energizer isn't enough, you must activate it for it to count. Activating the energizer counts towards another achievement, so it's good to use them when you get them.
There are five levels before you reach the final one which will pop this achievement. Each of the four levels will reward you for your effort and keep track of your amount used.
Energizers are bought using crystals. Crystals can be bought through the bank (actual money) or earned through leveling up (you get five each time). Energizers cost between 2 to 40 crystals.