Happy Gene is found in Worlds 4 through 6 in Magatsu Mandala within the Midnight Channel. It will try to afflict the party with status effects and its Galgalim Eyes skill can potentially reduce a party member's HP to 1 along with causing Enervation. After being defeated, it may drop Unthinkable Metal. Selling 4 Unthinkable Metal will unlock the Militia Dagger weapon for Yosuke Hanamura in the shop.
In Golden, Happy Gene has no offensive skills. It can erect both physical and magical barriers, sacrifice itself to heal an ally to full, or cure all ailments except for Down. It protects its weakness with Dodge Physical.
Persona Q2: New Cinema Labyrinth
Happy Gene in found in Area 4 of the second Theater, Junessic Land. It makes frequent use of Sukukaja to boost its accuracy and evasion. The Gene Fibers it drops can be used to acquire the Fern Whip for Ann Takamaki, Rubble Launcher for Morgana, Hard Rocker for Makoto Niijima, Dinosaur Legs for Chie Satonaka, Downpour Fan and Fortified Tessen for Yukiko Amagi, Kazegiri for Teddie and Primal Bikini female armor. The Gene Crystal that it drops is used to acquire the Obsidian Knife and Skinning Knife for the P5 hero, Fern Whip and Skin Ripper for Ann, Alpha Saber for Goro Akechi and Primal Naginata for the P3P heroine.