Kingdom Hearts III
In the boss battle, Marshmallow is not difficult, but can be tricky. His main attacks are two forms of a fist swipe. If he swipes twice if his fists, they can be blocked, but the second fist will trigger Risk Dodge. If he performs a double-fist clap, block and immediately counter. He can also jump to create a shockwave, which will trigger Risk Dodge. His third attack is breathing a gust of ice, which will freeze Sora if not blocked. It can be blocked, however, and if blocked, Sora should follow with a counterattack after the combo ends.
If hit by any Fire attacks, he will temporarily be stunned. Occasionally, Sora and Goofy will team up to perform the Tree Whip situation command, where as Marshmallow gets closer to them, they must fling the tree at him. Eventually, he will cover himself in spikes and his attacks are much more aggressive in this state. This form of him is armored. Luckily all his attacks can be blocked. It is recommended to block all his slashes, wait for him to pause, and quickly use Counter Slash to deal damage. Then immediately block his next series of slashes, and repeat until the armor is destroyed.
It is recommended to use Keyblades that have blocking abilities even during Formchanges. The Favorite Deputy is most recommended because it can deal high melee damage with the Hyper Hammer and the Drill Punch, while also having blocking abilities. Likewise, the Hero's Origin is also a good choice due to Counter Shield dealing insane damage with reprisals. Marshmallow is not the most difficult, and will fall with ease.
As a party member, Marshmallow uses the same attacks, except his spiked form is activated with the Mighty Avalanche situation command, where Sora rides on him as he attacks. During the battle against the Sköll, when it turns into a giant dark sphere Marshmallow helps Sora destroy it.