In Fighting Some ZZZ's, Unown was revealed to be the source of Will's ability to manipulate the Dream World. It was used to transport Will away at the end.
In Skirmish of Rivals! Confrontation in the Dream World, Unown distorted the Dream World to transport Will and bring him, Ian, Dakota and Steve to a Battle Royal arena. It was Will's second choice in battle, going against Ian's Staravia, Steve's Umbreon and Dakota's Bacchus the Espeon. Unown's Hidden Power is of the Bug type, allowing it to defeat Bacchus. It attacked Forest the Sceptile as well, but its attacks were intercepted by Staravia. After Steve chooses Charizard, Charizard beats Staravia then it and Forest collide with their strongest attacks. Forest survives, but Unown defeats it quickly afterwards. It is then defeated by Ian's Chimchar.
In Rise of the Sinister Six, Unown created a pocket dimension for Will to retreat into. When Mirage Master invaded, it attacked to defend against Mirage Master's Unown. Unown loses to its opponent.
In From Bad Dreams to Living Nightmare, Unown battles Tobias' Darkrai in the Dream World. It is put to sleep and effected by Bad Dreams, causing a cataclysmic chain of events that spreads to the Unown holding the dimension together, causing it to fade. It is eventually woken up, and defeated by Darkrai for good measure.
In Crisis in the Dream World!, Unown helps Will to alter space to create a stadium for his tournament. Will's Unown tries to attack Mirage Master's Unown, but is blasted back. It creates a Dream Tent so Professor Burnet can return back to the Dream World. It takes on a Dream Malamar belonging to Mysterio, its Hidden Power type allowing it to win easily. It later convinced Mirage Master Unown to stop attacking, and to allow Professor Burnet to capture it.
In Crisis Across the Multiverse, Unown was chosen to attempt to send Venometal back into Ultra Space. It remains out and teams up with Mirage Master and Alien X to open portals throughout the fragmented reality in search for Mewtwo.
