The Fusion Kart is a co-op, tank-like vehicle that is a prominent feature in Mario Kart Arcade GP DX. It appears only if either two players are playing in adjacent arcade cabinets and if they opt to play in co-op mode instead of against each other (Two-Player Co-op) or if there are 4 players playing and they wish to split into pairs (Team Battle), where the latter is exclusive to v1.04.
When a player obtains the special power-up via Item Box, an option to turn into the Fusion Kart is available. When one player from their team uses their item button in order to activate the Fusion Kart, the rear player instantly teleports to the front player (eventually gaining up to 4 positions in the process), and the players' karts fuse together to form a single large kart, called the Fusion Kart. The player who activated the Fusion Kart shoots while the other player drives; this concept is very similar to the double kart concept from Mario Kart: Double Dash!!. The shooting player has an infinite number of Green Shells and can shoot in any direction, including sideways and backwards. The transformation lasts for 17.5 seconds; the tank will flash blue when 4 seconds remain, and once the time limit expires, the two players split and resume driving as they were before. The shooting player faces the same direction as the driving player when the transformation ends, and there is a 0.6 second delay before the players can control their kart again. The Fusion Kart cannot be used by CPU players.
If the race ends with the Fusion Kart crossing the finish line before the transformation ends, then the player that is in front of their teammate before the Fusion Kart was activated will be credited as finishing in front of their teammate.
When playing with 4 human players in Team Battle (v1.04 only), the Fusion Kart also has a health bar. The Fusion Kart will only take damage when it is hit by shells; contact with items other than shells will destroy the item without damaging the Fusion Kart. After the Fusion Kart is hit by shells 3 times, the tank will flash red and after 4 seconds, the transformation will end and both players will crash as if they were hit by a shell.
Note: This feature is exclusive to the Japanese cabinets. In other cabinets, there are no Experience Points, and the Fusion Kart will always be Level 1 with each race.
By playing in Two Player Co-op or Team Battle (v1.04 only), the player can gain experience points to upgrade their Fusion Kart. As long as the player's team finishes 2nd or above in a race after the points are tallied up (see here), the player can earn experience points. The player earns more experience points when their team wins. In a Team Battle, if a draw results from one team finishing 1st and 4th with another team finishing 2nd and 3rd, all players earn experience points for the 1st position. By earning XP, the player can gain up to six levels of the Fusion Kart. Each level requires a different amount of XP and each level fires a different item. In addition, it also increase the attack and defense power of shells.
The list is as follows:
|Level||XP Required^||Total XP||Item Used|
|6||120||380||2 Koopa Shells|
- ^Amount of XP required to rank up to this level.
- The feature could have been inspired from the game Crash Tag Team Racing, whose main gimmick also involves two karts fusing, with one taking a first-person shooter reticle.