Boxing Plus is a Plus Event that appears in the Nintendo 3DS version of Mario & Sonic at the Rio 2016 Olympic Games. The objective of the event is to event is to be the first to knock out the opponent. The playable characters in this event are Mario, Bowser, Donkey Kong, Sonic, Knuckles, Zavok and Mii, with Zavok unlocked by beating him in the event on the sixth day of Sonic's story in the Road to Rio mode.
In this event, the player only plays a single match, being shown at the end to have already beaten another opponent. Before the match, the player must select a guard type, being able to choose from Auto Guard, which causes the character to constantly guard unless performing punches, or Manual Guard, which allows the player to move faster when not guarding. The match consists of two timed rounds, which is won by either knocking the opponent out, knocking them down three times, or by winning the decision that is made when neither character meets the requirements for the other two winning conditions, which is based on the number of times a character was knocked and the amount of damage dealt to the opponent. The player can move left and right using or , and can land punches when they are close enough to the opponent. The player can deal several types of punches using different buttons, with straight punches performed by pressing , jabs and hooks performed by pressing and guard breaking punches by pressing , which will break the opponent's guard and leave them open to punches, but also leaves the character that performed it vulnerable too. Over time, as the player lands more punches their Special Punch gauge will fill, and the player can press to perform a Super Punch, which will deplete a large amount of the opponent's health if it makes contact. The player can protect themselves from punches by guarding, done by pressing in manual guard mode, which prevents them from taking damage but will deplete their guard gauge instead. When this is fully emptied, the opponent can perform a guard crush, which will leave the other character vulnerable for a short period of time. At various points during the match, Item Boxes will appear in the corners of the ring, which the player can move towards to collect. Upon collection, the item inside will be used automatically, however the Item Boxes will disappear after a short while regardless of whether they have been collected or not. Each item has a unique effect:
If the player's health gauge fully depletes, they will be knocked down. If the player is knocked down either before or during the use of their item, the item and its effect are lost. If the player is knocked down, they must repeatedly press to get back up and fight on, however failing to press enough within the time will mean that the player has been knocked out and loses the match. Recovering becomes more difficult the more times that the player is knocked down.