Miasmo is the master of the Smogglings. He made the Smoglings send General Greenthumb to Exhaustia. He then changed him into Sergeant Smoggler. He lives in a factory in Exhaustia and is made out of smog. He commanded the Smoglings and Sgt. Smogglor to polute Parks and attack toys. Eventually, he gives permission to Sgt. Smogglor to use Smogglobs when it turns out his ZAPOW doesn't affect Chibi-Robo. When Smogglobs use gas on flowers, they become Miasmo Flowers, because they are named after him since he is gray like the flowers and is made of gas. When Sergeant Smogglor starts to turn back into Captain Greenthumb, Miasmo comes and changes him back into Sergeant Smogglor and allows him to use a SUPEREXTREMEZAPOW. Later when he changes back again, Miasmo does the same thing except he allows him to use a SUPERELITEZAPOW. When Sergeant Smogglor turns back into Captain Greenthumb for the last time, Miasmo changes a lot of flowers into Miasmo Flowers. When the Park gets 1000 flowers, the next day, Miasmo commands the Smoglings to send Chibi-Robo to Exhaustia. There Miasmo battles Chibi-Robo. General Greenthumb jumps on him late in the battle and starts tickling him. Once he is defeated, Chibi-Robo will return to the park.
Miasmo initially sends several Smoglings after Chibi-Robo. Defeat the Smoglings to cause seed to get planted. If a Flower is grown, a Happy Point will appear and fly into Miasmo causing him damage. Throughout the fight, Miasmo will occasionally change a lot of Flowers to Miasmo Flowers. He regains health whenever there is Miasmo Flowers, but turning a Miasmo Flower back to normal will cause a Happy Point to appear and fly into Miasmo. Eventually, he sends out a Smogglob. Defeating it will cause many seeds to appear. Once he has ten health left, General Greenthumb jumps on him and starts tickling him, preventing him from turning flowers to Miasmo Flowers. Once he has no health left, he vanishes.