Combo Boost

Combo Boost (コンボアップ/コンボブースト), is an ability found in Kingdom Hearts Re:Chain of Memories, Kingdom Hearts II, Kingdom Hearts 358/2 Days, and Kingdom Hearts III. It increase the damage output during physical attack combos. In Kingdom Hearts Re:Chain of Memories, it also grants resistance to fire, ice, lightning, and special attacks.

Kingdom Hearts Re:Chain of Memories
In Kingdom Hearts Re:Chain of Memories, Combo Boost is an effect of Saïx's Enemy card which lasts for 20 attacks. The Black Fungus Enemy card can activate Combo Boost with its effect Random Flush, and the Darkside Enemy card can Mimic an opponent's Combo Boost.

Kingdom Hearts II
In Kingdom Hearts II, Sora obtains the Support ability Combo Boost at level 9 with the Dream Shield, level 7 with the Dream Sword, or level 17 with the Dream Rod. Combo Boost costs 5 AP to equip in Kingdom Hearts II Final Mix or 3 AP in Kingdom Hearts II. Sora can also obtain Combo Boost by equipping the Decisive Pumpkin.

The damage output of Combo Boost follows the formula M=1+(c*n):
 * M is the amount that gets multiplies to each ground finishing move's damage. To clarify, if Sora has more than one ground finishing move, they all gain the effect of Combo Boost.
 * N is the number of attacks in the total combo. While the first finishing move counts toward this value, consecutive finishing moves do not increase this value.
 * Every Combo Boost equipped adds 0.1 to C. Since Sora can only obtain one Combo Boost by levelling (0.1) and one Combo Boost by equipping Decisive Pumpkin, (another 0.1) the maximum total for C can be is 0.2.

Kingdom Hearts 358/2 Days
In Kingdom Hearts 358/2 Days, certain weapons have Combo Boost as an ability when linking an ability panel.

The Soldier Ring also has Combo Boost as its equipment ability.

Kingdom Hearts III
In Kingdom Hearts II, Sora obtains the Support ability Combo Boost at level 46 with the Power of the Mystic, level 36 with the Power of the Guardian, or level 20 with the Power of the Warrior. Combo Boost costs 5 AP to equip. Sora can also obtain Combo Boost by equipping the Ultima Weapon. It increases the damage of each hit in a ground combo by (number of hits) x 5%.