The Nu can be found in the Cursed Woods of Middle Ages, the Hunting Grounds of Prehistory, and at Enhasa in Antiquity. At the Cursed Woods and Hunting Grounds they only appear when it rains. Nu work as merchants or assistants during 12,000 B.C. A single Nu can also be found in the Present at the Forest Ruins and another one in the Future era as Belthasar's assistant. the Nu can be found scattered throughout all time eras except The End Of Time unless Spekkio as a Pink Nu is counted. Other Nu include Nu Guardian, Nu Master, and the Pink Nu.
Nu has two Head-Butt attacks, one which reduces a character's HP to one point, and another which does exactly only one point of damage.
As soon as you have access to the Hunting Grounds, team up as Crono, Marle and Lucca. Hit the Hunting Grounds and kill a few monsters until the rain begins. Run over to the Nu's spot (southeast corner of the map, second level; or northeast corner, first level) and fight the Nu. while Using Crono & Lucca's Fire Sword attack (this will do around 500dmg), and have Marle wait until the Nu attacks. Use Marle's Cure on whoever he just attacked, then repeat the process with Fire Sword. After the Nu has been struck twice by Fire Sword, you can resort to normal attacks (should only take one or two).
Alternatively, if Crono , Frog and Robo have learned Triple Raid, it will do approximately 1,000 damage to the Nu. Start with this then follow with two regular attacks. Use Robo's Cure Beam after the match to heal whoever needs it.
The Nu can be found in Prehistory and can be a good source of Tech Points early on in the game. They're also a good source of the ingredients needed to purchase the equipment at the Ioka Village Hut. However, Nu only appears when it rains. You must find Nu before the rain stops. If you do not, then Nu will leave until the next rain. The first time you defeat the Prehistory Nu, he rewards the party with a Third Eye.
In the secret room of Enhasa, there are six Nu. Each will attack random party members with one of the two Head-Butt attacks.
There are a few Nu working as merchants in Antiquity era, Arena of the Ages, and Black Omen. There is a single Nu in the Laruba Village that can change any character's name. And another Nu can be found inside the Northern Palace. and two Nu that appears in the Black Omen does different things to assist you. The one on the left lets the character buy and sell things, while the Nu on the right offers to let the player leave the Black Omen.
At least one Nu was built by Belthasar. In the Future era, this robotic Nu helps the Guru build the Epoch. This Nu is also found in the Present at the Forest Ruins, expecting Belthasar to return soon after waiting for 13,000 years. Before Belthasar's death, he programs the Nu with his memories and the Nu gives the team the time-traveling airship, advises the team to find a Doppel Doll to help revive Crono, and then sends three special Poyozo Dolls to Death Peak to help them scale it. while A second Nu specifically mentions him. It is unclear whether or not all Nu were built by him. If they were, their presence in each time era outside of Antiquity could be explained by the same rifts that transported Schala, Janus, and the three Gurus (although considering the one is the Forest Ruins had, according to it, lived 13,000 years, it is also highly probable they just never died off. This is expanded on, by the comment written in the Mystery of Life, that Nu was the origin of life on the planet).
Belthasar's Nu assistant seems to have carried over, as a BeachBum (thought to represent a Nu) resides in the library of Viper Manor where the Neo Epoch is kept. He can also change the names of the team members of Serge's party. It is apparent that a Nu was at one time planned to be a playable character; its dialogue icon appears in the Chrono Cross Demo disc's data and its design is distinctly Nu (not BeachBum).
Alongside a Poyozo named Mamo, a Nu tries to recruit members for their group "Nuumamonjaa". Finding no one willing to join them, they wander the fair and interrupt the robot Johnny's show. Attempting to win a golden shovel at the Fast-Drinking Contest in Leene Square, Mamo volunteer's the Nu; it is quite clear that the Poyozo pushes the Nu around. During the game, the Nu tips the table and drinks every glass in one drink, the nu quickly becoming full. The Poyozo proceeds to plug a SNES controller into the Nu to take control and win the game. This scene seems to support the notion that all Nu are robotic.