When the Winx begin their third year at Alfea, they are told about their final Enchantix transformation as well as its additional powers it gives to fairies such as the use of fairy dust and the ability to Miniaturize themselves. Once the Winx gain their Enchantix, they are able to use their Miniaturization power except Bloom, whose Enchantix was incomplete since she gained it out of her will, not by saving someone.
The Winx, minus Bloom, used this power numerous times throughout the season, such as in "Crystal Labyrinth", to enter the Golden Kingdom, and in "A New Beginning", to escape when all the water of Lake Roccaluce was returning back to its place after Bloom temporarily defeated Valtor.
The Winx Club were forced to use their miniaturization powers to gain access to the Tree of Portals so they could find a way of entering the realm of Obsidian. Only Bloom was incapable of entering because of her willed-on and therefore incomplete Enchantix.
The Winx used it two times. Firstly, when they used it in "The Tree of Life" to be small enough to enter Pixie Village, which was Bloom's first use. In "The White Circle", they used it to get away from the Wizards of the Black Circle, and to help Roxy who was about to be attacked by the Wizards.