This is about the version of the character seen in The Snow Queen, and is not connected to the film version.
Marshmallow is a large snowman and a supporting character in The Snow Queen. Marshmallow was created by Elsa during the eighteen years she lived alone on the North Mountain. He is the "little" brother of Olaf and Beatrix, and is much less intelligent than his two siblings. Unlike the film version, who is voiced by Paul Briggs, this portrayal of the character is voiced by Vin Diesel.
Marshmallow's appearance isn't too dissimilar from his film counterpart. A hulking behemoth of a snow man, Marshmallow's arm and leg joints are comprised of ice rather than sticks, unlike Olaf and Beatrix. His fingers are made from rounded icicles and are really sharp like knives, his elbows and knees having sheets of ice on them like knee and elbow pads. When angered, the film version of Marshmallow's eye sockets light up demonically and ice spikes will protrude from multiple parts of his body. It is currently unknown whether or not this iteration of the character possesses this ability, due to the character not yet being shown to lose his temper.
Unlike his aggressive, territorial film counterpart, this version of Marshmallow seems much friendlier than other versions of the character. He is a close friend to Elsa, and also seems to have befriended Anna during their meeting on the North Mountain.
Due to his larger size and smaller brain, he is slightly clumsier and less intelligent than Olaf and Beatrix, and often speaks less articulately than they, though still speaks more than the film version. Like his siblings, Marshmallow enjoys watching the Spring Festival, and initially suggests that he, Olaf and Beatrix accompany Elsa to the festival when she is reluctant to go.
Despite his low intellect, Marshmallow is shown to be a talented singer and piano player, as seen in Chapter four when he is able to hit a powerful high F note when singing alongside Olaf and Beatrix.