The Mushroom XIII are a group of thirteen Mushroom Heartless that wear Black Coats which appear in Kingdom Hearts II Final Mix. Like all Mushroom Heartless, they each require special treatment in order to be properly satisfied. The mini-games required to defeat them are recorded in Jiminy's Journal.
Once defeated, a Mushroom will drop one of the Tranquil materials, which are designed after the Mushroom XIII. In addition, the six even Mushrooms will drop shields for Goofy, while the six odd Mushrooms will drop staves for Donald Duck. Fulfilling the highest requirement for each Mushroom will also reward the player with the Premium Mushroom for the odd Mushrooms and the Limited Mushroom for the even Mushrooms. Unlike the others, the thirteenth Mushroom drops not a shield or a staff, but the Winner's Proof Keyblade and a Tranquil Proof.
All of the Mushroom XIII Heartless share a common appearance. They all sport the same spherical, pitch-black heads and glowing eyes, and they all wear black coats reminiscent of those worn by Organization XIII. These coats are black and sport similar zippers, pull-strings, and hoods—the latter of which resembles a mushroom cap and has two angular, black spirals decorating it. The Heartless emblem is displayed on the front of all of their coats. The members of the Mushroom XIII only differ in two regards; the numbers on their backs and their size. Each Mushroom XIII member has a different silver Roman numeral from I to XIII on their backs, representing their rank. The members' sizes can vary greatly. No. V is the largest and is larger than Sora, while No. VIII is the smallest, and is roughly half of Sora's height.
The Mushroom XIII's collective name reflects their mushroom-like shape and their resemblance to Organization XIII.
 List of members
 No. 1
No. 1 appears at Memory's Skyscraper after Xemnas is defeated. In order to defeat it, you must hit it 70 times within 30 seconds. In order to get the Premium Mushroom, you must hit it 99 times.
Like Xemnas, this Heartless has the "Reversal" reaction, and its large size is a reference to Xemnas' role as the leader of Organization XIII. In addition, its location is a reference to the first fight against Xemnas, which takes place in Memory's Contortion.
It is recommended to use Wisdom Form to defeat No.1, since it has quick attacks, and you can land at least three hits with the Shoot function. Final Form is very useful too. With one jump and an attack you can land 9 hits.
 No. 2
No. 2 is in Christmas Town, where you fought The Experiment. You must dodge or block its projectiles until your score reaches 80. Final Form is highly useful for No. 2, since almost every action made in Final Form also guards Sora from external attacks, and the projectiles can be blocked.
Like Xigbar, it shoots projectiles that must be deflected.
 No. 3
The prizes may reference the opportunities for Sora to use the Learn and Jump commands from Xaldin in his boss fight. The location of the mini-game also references Xaldin.
 No. 4
No. 4 is in The Land of Dragons, outside of the Palace. You must have defeated Shan-Yu to reach No. 4. You must hit 85 of the clones without getting hit once. A recommended strategy is to hit the first batch of clones normally, and then use Final Form to fly around and ram into the clones with the spinning Keyblades or using Thundaga with the Photon Debugger equipped. The Form may run out near the end of the duel, when the clones are stronger, so the player should keep a distance and use Thundaga to kill the last few clones and reach 85.
 No. 5
No. 5 is in the Cave of Wonders, at the Treasure Room. Many would say that this is probably the easiest one to beat. You must defeat it in 10 seconds, although its health regenerates quickly. For its fast attacks, Master Form is best used when defeating No. 5, as this gives it less recovery time. Limit Form's Zantetsuken ground combo finisher is also extremely helpful, as it can easily chop away an entire bar of the Mushroom's health. Another strategy is to use Final Form, equip Fire Boost and Bond of Flame, and keep attacking with Firaga.
Its regenerating health is similar to the Power Meter of the Lexaeus Absent Silhouette battle. It is also the largest of the Mushrooms, narrowly exceeding No.1, also referencing Lexaeus' size compared to the other Organization members.
 No. 6
The clones are reminiscent of the boss battle against Zexion in the Reverse/Rebirth mode of Kingdom Hearts Re:Chain of Memories.
 No. 7
No. 7 is in Twilight Town, within the Tunnelway. You must defeat it in 10 seconds. However, coming in contact with the Mushroom will send a character flying. This trait is similar to the Berserk state of Saïx.
The key to taking No. 7 out is by using long-range attacks. Wisdom Form works well, though the player will have to keep gliding away from No. 7. Alternatively, you may use Limit Form's Sonic Blade, Strike Raid and Ragnarok combos to keep it at bay. Final Form and Reflega is another extremely effective method.
 No. 8
No. 8 is in Twilight Town, outside Yen Sid's Tower. Many say that this is the hardest challenge: bouncing the mushrooms around like a ping-pong ball 85 times, similar to the Rare Truffle in the first game. A way to make this easier is to equip Berserk Combo, repeatedly press Thundaga until MP runs out, then keep hitting it over and over. When MP is refilled, repeatedly press Thundaga again. Make sure to remove all MP Haste abilities.
It is similar to the Overtake/Clear Light Reaction Command in Axel's boss fight in the 6th Day of the Prologue.
 No. 9
No. 9 is in Radiant Garden, where you fought Demyx. You must hit it 75 times without letting it stop spinning. This can be accomplished by attacking with the Fatal Crest, Berserk Charge and Horizontal Slash equipped, a combination which can land up to 99 hits.
The Mushroom's spinning, or dancing, is a reference to Demyx's association with music and control of Dancer Nobodies. Also, it is the location where the Melodious Nocturne met his end.
 No. 10
Finding the real one amongst fakes references Luxord's boss battle and the shuffling of cards.
 No. 11
No. 11 is in Timeless River, in the waterway. You must deplete the hit counter above its head in 19 seconds.
The hit counter resembles the one Marluxia uses against Sora in his Absent Silhouette battle. The best way to defeat it is by using Wisdom Form, combined with the Fenrir Keyblade, Negative Combo and taking off all Combo Plus abilities.
 No. 12
No. 12 is in Twilight Town, outside the Old Mansion. You must defeat all of the clones before time runs out. However, unlike No. 6, they appear by themselves in rapid succession.
The clones' rapid appearance reference Larxene's Absent Silhouette battle.
 No. 13
No. 13 is in the Great Maw in Radiant Garden (where you fought the 1000 Heartless.) You must have beaten all of the other Mushrooms to reach the last Mushroom Heartless. You also gain a crown.
Its non-hostility compared to the other twelve references Roxas as being unusual compared to the rest of the Organization. Also, it comes down to you with a beam of light, a possible reference to Roxas's element of light.