Magwai, Mogwai, Mogui or simply Gui is the transliteration of the Cantonese word 魔怪 (Mandarin Chinese: 魔鬼; pinyin：móguǐ) meaning "ghost", "evil spirit", "devil" or "demon".
The term "mo" derives from the Sanskrit "Mara", meaning 'evil beings'. In Hinduism and Buddhism, Mara determines fates of death and desire that tether people to an unending cycle of reincarnation and suffering. Meanwhile, "gui" does not necessarily mean 'evil' or demonic spirits. Classically, it simply means deceased spirits or souls of the dead. Nevertheless, in modern Chinese, it has evolved to refer usually to the dead spirits or ghosts of non-family members that may take vengeance on living humans who caused them pain when they were still living.
The Gui wear clothes which have no hems, and their bodies cast no shadows. People can only perceive them as a breath of air. To these ghosts, humans are only perceived as a dim red light.
Mogwai are are said to reproduce sexually during mating seasons triggered by the coming of rain. Supposedly, they take care to breed at these times because rain signifies rich and full times ahead. It is common for the living to redress their sins by sacrificing money to gui by burning (usually fake) paper banknotes so that gui can have funds to use in their afterlife.
Mogwai in the Gremlins series
As depicted in the 1984 Joe Dante film Gremlins and its 1990 sequel Gremlins 2: The New Batch, the word mogwai is used by some Chinese characters to describe a rare sentient being as it is a furry, cute, good-natured creature.
There were 'three rules' that are known to keep a mogwai--- if exposed to water, it immediately reproduces more of its kind asexually by budding from its back; if it eats food after midnight, it will transform into a cocoon, going through changes and, given the circumstance, becomes a ferocious, reptilian monster called a gremlin. Sunlight will kill a mogwai (like a vampire) and bright light is known to hurt it. Most of the mogwai creatures are mean-spirited and mischievous, with Gizmo, the most famous mogwai, being a rare exception.
The level of maliciousness in the personality of mogwai and gremlins vary. Some like Stripe (the main antagonist of Gremlins), Brain (one of the gremlins turned intelligent in Gremlins 2), and Mohawk (the primary antagonist of Gremlins 2 who is reincarnated from Stripe) are exceedingly violent and show great delight in hurting others. Others like the Christmas carolers, and the flasher, just delight in scaring people and causing hijinks. All mogwai (even Gizmo) are also energetic and extremely curious, the latter quality often getting them into trouble.
Mogwai are also pack minded, following a leader who is dominant but also has a quality that differentiates them from the others of their kind. Examples of this come from the primary mogwai/gremlin leaders: Stripe, Mohawk, and Brain. Stripe and Mohawk both had a strip of fur the others didn't, but were more violent and more dominant than their species. Brain was originally a normal gremlin but after his transformation became much more intelligent then the rest of his kind and replaced Mohawk as the leader (without any form of conflict, mostly concieved from Mohawk staying behind to torture Gizmo as revenge).
Little else is revealed about the mogwai's biology. In Gremlins 2 Gizmo is taken to a laboratory, where the scientists speculate that mogwai are rodents. However, when confronted with gremlins, they believe that the gremlins are reptiles or viruses. The scientists also note they are uncertain as to whether Gizmo's cuteness is genetic. They also explain Gizmo's fear of bright lights by calling it an allergy.
In the novel Gremlins, by George Gipe, published by Avon Books in June 1984, it is stated mogwai were created as gentle contemplative creatures by a scientist on an alien world, and that the transformation into gremlins was an unintentional side-effect.
Also, in the novel, it is stated that for some reason, mogwai are now almost always born mischievous or just plain evil, with a very rare (1 in a thousand) gentle one (such as Gizmo) viewed as an anomaly and hated by other mogwai. The book also states that there are 3 other "minority" mogwai on this planet, hinting that they were once plentiful.
The Scottish post-rock band Mogwai is named after the creatures who make an appearance in the film Gremlins, although the guitarist of the band, Stuart Braithwaite, comments that "it has no significant meaning and we always intended on getting a better one, but like a lot of other things we never got round to it." 
- Qiguang Zhao, "Chinese Mythology in the Context of Hydraulic Society," Asian Folklore Studies, Vol. 48, No. 2 (1989), pp. 231-246.
- Jacques Gernet, 'China and the Christian Impact: A Conflict of Cultures'; originally published as 'Chine et christianisme: action et réaction' (1982). 25.