Mushu is a small but tough noodles dragon with a sense of humor who is one of the characters in Spongeob and Friends meet Mulan. He is the titular character's closest companion throughout the Mulan series, and the Spongebob and Friends siries, acting as Mulan's guardian and protector, and a member of the Shell Louge Squad. he's like that fun and caring brother to the louge, but sometimes quick to really panic when it seems like the end.
Mushu was once a guardian spirit of Mulan's family, but he has been demoted to the humiliating position of an incense burner and gong-ringer for the deceased Fa ancestors ever since he failed to protect a family member, a soldier named Fa Deng, resulting in the soldier's demise by decapitation (he's seen carrying his own head as a spirit).
In contrast to Mulan, Mushu is in most situations more comical, overconfident, and impulsive. He strives to be one of the family guardians again, and selfishly decides to convince Mulan to join the army to turn her into a war hero, believing this will get him back on the 'top shelf'. However, he comes to realise how selfish he has been, admitting to Mulan that he risked her life to further his own goals. He then intends to take her home to face the consequences of his actions, but when she insists on stopping the Huns and villain leagers, loyally follows her, showing that underneath, he has a good heart.
Mushu is rather sensitive about his size.
Mushu does not resemble a Western dragon much. Eastern dragons could control many elements and did not require wings to fly. His appearance is far more akin to that of a traditional Eastern dragon. Mushu's element (presumably to reassure the viewers that he is a dragon) is fire. However even the Great Ancestor himself does not consider Mushu to be a 'real' dragon - he is very small, about the size of a lizard, and his fire-breathing ability is less than impressive, and he's more useful as an emergency firelighter than as a weapon. As a mythical creature, Mushu is very durable, to the point of being seemingly immortal. He endures being stomped on, explosions, and an avalanche in the first movie. He can also understand other animals, as seen when he converses with Cri-kee (Mulan's lucky cricket) and horse Khan. At one point when he wants to disguise as a soldier riding a horse, he finds and persuades a panda bear.
At the start of the film, Mushu does not make his official appearance until after Mulan runs away from home, along the shell lougers, to serve in her elderly father Fa Zhou's place in a war against the deadly Hun army and the villain leage. Knowing that Mulan's exposure will lead to the disgrace of the Fa family, the spirits of the ancestors choose to send Mushu, on a bet Mushu made that if he could make Mulan a hero, they'll make him Guardian again.
In the coming soon sequel, when Mulan prepares to marry Li Shang, Mushu is at first overjoyed to the point of tears, going as far as planning the wedding himself. However, things change once the ancestors tell him that if Mulan marries Shang, his family's guardians will take over for Mulan, thus making Mushu a homeless dragon. the ansisthers will even forever forbid Mushu to continue his work with the shell louge squad. Desperate to keep his job, and to ensure he gets to remain a shell louger, he continuously tries to break the two apart to keep his position. but it has not gone un-noticed by Shifu and Cynder. But as the film goes by and Mushu grows even more desperate to keep his job, Fagin siezes an oppurtunity to try and corrupt Mushu into falling off the slippery slope to darkness, and thereby betraying Spongebob, killing him and giving Fagin his soul if the presicution of Shen and Cynder in Ki-Gong plan backfires. But but eventally, Mushu's good heart and regret prevents such a thing, as well by his redemption by pretending to be the Golden Dragon of Unity right before Mirage branded Spongebob the Ultimate Vigilante and he, Kairi and Spyro become the UU's Most Wanted.