This feature is unobtainable and can only be obtained via hacking.
This article lists all features that are currently unimplemented. It does not include features that were once in the game but were eventually removed (such as Serial Codes).
Chicken Cat was an Uber Rare Cat that was part of a scrapped collaboration with Nobe_tto (のべぇ〜っと), creator of "Life of Chicken and Chicks". It was never obtainable through any means, and was eventually removed altogether in Version 8.7.
673-1 is an Uber Rare Cat added in version 11.7, with useless stats and no evolution. It appears to be a cheetah with a Cat face and a ball chained to one of its legs, and its Japanese name is Neko Chītā (ネコチーター), which can be translated as either "Cheetah Cat" or "Cheater Cat". Since it can only be obtained by cheating, that may in fact be the joke.
Unused Ancient Eggs
Enemy IDs 21 and 22
Enemy ID 21 shares Zoge's (ID 286) sprites and animations, but has completely different stats. This enemy slot has always been unused: it and ID 22 separate The Face at ID 20 from Ms. Sign at ID 23. It seems that the slot was used to test Zoge's animations, and the developers simply forgot to delete the unused data. Also, in previous versions, the image file for this enemy housed a red Master A. recolor named "Bloodsucker"; this was presumably an early version of Professor A.
Enemy IDs 566 to 571
Enemy IDs 566, 567, 568, 569, 570 and 571 share Doge's stats, sprites and animations, but are traited as Aku. Since these IDs come right after Wicked Cat, Wicked Tank Cat and Wicked Axe Cat, it is possible that they are stand-ins for Wicked versions of the other six Normal Cats.
Unused Unit Sprites
Mr. and his evolved form, Super Mr., use the same spritesheet internally, even though Mr. carries a shotgun while Super Mr. uses a bazooka. Also, the spritesheet has an unused missile in it. This same missile would later be used in Tricycle Cat's spritesheet.
Tricycle Cat's spritesheet includes an unused greyscale version of the missile he normally shoots in his attack animation.
Biker Cat's spritesheet has considerably more unused sprites than his pre-evolution, including three unused missiles, a sonic boom, and a red version of the spikes he normally ejects from his front wheel to attack. It seems that he was originally meant to fire a much bigger missile than his pre-evolution; the missile is still present on the in-game model, but does not animate and is set to 0% opacity.
Cat Base Mini
All three members of the Cat Base Mini evolution line have unused sprites. Cat Base Mini and Cat Base Jr. both have duplicates of the wave effect from the Cat Cannon. In-game, both of them instead use the same wave effect as every other unit.
Cat Base Ultra
Cat Base Ultra doesn't have the unused wave effect, but it does have an unused Li'l Cat head present. It's unknown where it would have been used, as it's too big to fit inside the base's door or the top port.
The spritesheet for Drumcorps Cat includes sprites for two additional Cats, a tuba, drumsticks, and particles relating to them. However, in-game, only the leading Cat with the baton is used.
Kachi-Kachi's spritesheet has one more unused frame of animation for the tanuki in the top-right corner.
Supercat's spritesheet includes four rectangles, coloured dark yellow, cyan, magenta, and dark green, respectively. These are not assigned to any parts on the model. Strangely, they're also nowhere to be found on the spritesheet of Mightycat, the first form.
There's an unused impact effect on Bakery Cat's spritesheet. Technically, the sprite is used during gameplay; however, it's set to 0 opacity, so it never renders during the attack animation. It also appears on Boomerang Cat's spritesheet, where it "animates" in the exact same way.
"Floating" Metal Cyclone
Metal Cyclone was one of the few enemies to go unused in the game files for an indeterminate length of time before it was implemented. When hacked into a stage, it would appear to float above the ground rather than grinding against it.
Pre-Release Teacher Cybear
Teacher Cybear is another example of an enemy that was unimplemented for a while - until version 8.0, no less. Before he was implemented, Teacher Cybear was a Traitless enemy with 1,000 HP, 80 damage, 150 range, 15 speed, no abilities, no energy wave in his attack animation, and a money drop of 55,000¢, as seen in this video.
Bronze Cat Base
An unused enemy base featuring Bronze Cat can be found in the game's files, suggesting that Bronze Cat was originally a Monthly Event unit or that Cyclone Stages were originally going to have their own bases.
There are three types of Catfruit that are not used in-game. When hacked into the Catfruit Storage, the unused types only show as white circle with the kanji "仮" (meaning "temporary") written over it in BCJP, or as black boxes in other versions. When exchanged, they give 500,000 XP each.
Early Prelude to Ruin Background
The background used in Prelude to Ruin was added in version 10.0, but had a different color scheme closer to that of the one used in Saint Red Fox. Incidentally, this was the same update that added placeholders for a Legend Cat and an enemy named コニャンダム亜種 Ko Nyandamu Ashu ("Li'l Nyandam Variant"); their IDs would later be taken by Stone Cat and Evil Emperor Cat respectively.
Original Traitless Icon
There was no way to filter for abilities affecting Traitless before version 11.2, but from version 8.0 to version 11., a "W" ("White") icon could be found in the game's files among the many other trait icons.
Alternate Nebaaru-kun and Nyanpazuru Lucky Capsule
Cat Base With Hidden Doge
その１ (Sono 1, lit. "Part 1") was the placeholder name for an unfinished stage which cost 150 energy to play. The only enemies known to appear were Cruel Angel Clionel and Gentleman Bros., who spawned together at the beginning to form a nightmarish combo in which Clionel would annihilate your backlines and Gentleman Bros. would freeze anything that could enter her blind spot. It later became Old Master (Expert), with which it shared an ID.
Within the game's code, Imminent Disaster has five additional stages that are the exact same as those found in Here Be Dragons, minus Pilaf Field; while Unleashing the Cats has a mirror of Taking the Stage (Insane).
Weak Yet Bitter
The names of sub-chapter 28 and its stages could be found in the game date for an indeterminate amount of time before they were implemented. The stages' names were no different, but the sub-chapter was originally called Weak Yet Bitter, which was changed to Weak & Mildly Acidic on its release.
Certain region-exclusive units and stages (including collab ones) exist in the files of all versions, but with their sprites removed. Some use placeholders for their names and descriptions, but others have official translations.
To the Future and Droid Awakens!
The Battle Cats Together! and Cat Bros
The Battle Cats Together! is a Nyanko Daisensou-exclusive tie-in event with The Battle Cats Unite! that drops Rare Cat Cat Bros. Even though The Battle Cats Unite! has not released outside of Japan, both the event and the units have existed in all versions for years.
Note: "The Battle Cats Together!" was the original name for The Battle Cats Unite! before it was localized.
Unused Ability Variables
The Knockback and Savage Blow abilities have variables for distance and damage multiplier, respectively, but these are never utilized in-game: Every unit with knockback pushes enemies back the same distance and Savage Blows always deal 3x damage.
Although they were implemented in version 6.5, audio and sprites for Barriers could be found in the game's files as early as version 6.3. The pre-release Barriers had a different design, which most notably was blue instead of red; this may have been changed so that they would be easier to see against the already-blue skin of their Alien bearers.
Warp Resistant and Improved Knockback
Unused Enigma Maps
Only three Enigma rarities exist in the game, but sprites for two more can be found in the game files, as well as a platinum Enigma in the first image for the Enigma Stage tutorial. The former two may have simply been the original designs for Normal and Superior Enigmas.
Traitless and Relic Talent Orbs
Unused Aftermath Soul Sprites
The Aftermath soul has two unused eye sprites, for a partially-closed and fully-closed eye. In the final game, its eye always stays open.
Unused Talent Costs
There are two unused costs for Talents that max out at level 1: 150 and 250 NP. It is unknown what these are meant for, as the most expensive non-upgradable Talents are for Uber Rares, costing 100 NP.
Unused Combo Sizes
|Attack Up||L||Attack +20%|
|Attack Up||XL||Attack +30%|
|Defense Up||L||Defense +30%|
|Defense Up||XL||Defense +50%|
|Cannon Start Up||L||Start at 60%|
|Cannon Start Up||XL||Start at 100%|
|Worker Start Level Up||L||Wallet Lv +3|
|Worker Start Level Up||XL||Wallet Lv +4|
|Starting Money Up||XL||Start with 2000¢|
|Cat Cannon Power Up||L||Cannon Damage +100%|
|Cat Cannon Power Up||XL||Cannon Damage +200%|
|Cannon Recharge Up||L||Cannon recharge 15s faster|
|Cannon Recharge Up||XL||???|
|Worker Cat Max Up||L||Wallet Max +30%|
|Worker Cat Max Up||XL||Wallet Max +50%|
|Cat Base Defense Up||L||Base Health +100%|
|Cat Base Defense Up||XL||Base Health +200%|
|Research Power Up||XL||???|
|Accounting Power Up||L||Money Loot +30%|
|Accounting Power Up||XL||Money Loot +50%|
|Study Power Up||M||XP +15%|
|Study Power Up||L||XP +20%|
|Study Power Up||XL||XP +30%|
|"Strong" Effect Up||L||Ability Effect +30%|
|"Strong" Effect Up||XL||Ability Effect +50%|
|"Massive Damage" Effect Up||L||Ability Effect +30%|
|"Massive Damage" Effect Up||XL||Ability Effect +50%|
|"Resistant" Effect Up||XL||Ability Effect +50%|
|"Knockback" Effect Up||L||Knock Distance +30%|
|"Knockback" Effect Up||XL||Knock Distance +50%|
|"Slow" Effect Up||L||Ability Duration +30%|
|"Slow" Effect Up||XL||Ability Duration +50%|
|"Freeze" Effect Up||L||Ability Duration +30%|
|"Freeze" Effect Up||XL||Ability Duration +50%|
|"Weaken" Effect Up||L||Ability Duration +30%|
|"Weaken" Effect Up||XL||Ability Duration +50%|
|"Strengthen" Effect Up||L||Damage Boost Effect +50%|
|"Strengthen" Effect Up||XL||Damage Boost Effect +100%|
|"Critical" Rate Up||L||Critical Chance +3%|
|"Critical" Rate Up||XL||Critical Chance +4%|