"The Mysterious Hand" is not an official name. It may have been referenced by ids5621 as such, but has not been officially named. Alternatively, it may be a name popular among fans, but has no official basis.
While waiting in line to eat at the Tohunga Burger drive thru in it's MVT, Imutii had begun taking his order in front of him. However, The Mysterious Hand grew impatient and began honking at Imutii, causing the Matoran to exit his MVT and knock on The Mysterious Hand's MVT. Because of this, The Mysterious Hand opened it's MVT's front hatch and absorbed Imutii, seemingly eating him. This would not be permanent though, as Imutii later appeared again.