Holo Defense API is made up of four crystals surrounded by floating tablets, which spin around it. All four crystals have a bi-colored appearance; one is white and yellow, one is red and purple, one is teal and light blue, and the last is two shades of orange.
In The True Arena and Meta Knightmare Returns, an upgraded version called Holo Defense API 2.0 appears. This version has blue tablets and cross-shaped crystals, along with a few color changes; the first crystal's white side and the last crystal's lighter orange side has been replaced by a silver color.
Holo Defense API mainly fights by summoning green, holographic versions of bosses from previous games in the Kirby series. Each boss is associated with one crystal - when it is destroyed, the corresponding crystal explodes, leaving only a wireframe outline of itself. All of the holographic bosses are weaker than their normal counterparts, although they compensate by attacking Kirby one after another.
Summoned by the yellow and white crystal. Holo-Kracko's attacks and appearance are similar to Kracko's boss battle in Kirby: Triple Deluxe. It shakes itself and drops a Waddle Doo into the arena, turns grey and unleashes a swirl of blue beams that spiral around itself for a short time, followed by swooping down to the opposite side. Other attacks include showering Kirby with rain, moving along the top of the screen while shooting electricity, and moving along the bottom of the screen.
Holo-Kracko is the third and final Holo-Boss to be refought in Access Ark Stage 5.
Summoned by the purple and red crystal. Holo-Doomers look like the Sphere Doomers in Kirby's Return to Dream Land, specifically the Regular Doomer and Fire Doomer. They are fought in a similar manner to the dual Doomer fight from The Arena of said game, and attack by shooting fireballs or swooping at Kirby. They can use a dive to sweep across the stage, and they can fire orbs which travel in a straight line. The red ones can be swallowed for the Fire ability.
The Holo-Doomers are the first Holo-Boss to be refought in Access Ark Stage 5.
When Holo-Ice Dragon falls, the Holo Defense API alters the background to reveal five large pillars. Next, the orange and ochre crystal summons Holo-Coily Rattler, who acts similarly to his Kirby: Triple Deluxe counterpart. Unlike the other Holo-Bosses, he takes no damage unless an attack strikes his head, which appears blue. It fires three burning rocks from its mouth aimed at Kirby. These can be swallowed for the Spark ability. It can also do this move from the background. Then, it snakes its way across the stage, covering much of the ground with electric sparks. After that, it curls up into a ball and rolls across the stage. On the underside, it then turns around and rolls back onto the stage.
Unlike its fellow Holo-Bosses, Holo-Coily Rattler is not refought in Access Ark Stage 5.
Once the four Holo-Bosses are defeated, the Holo Defense API attacks directly. Emitting constant sparks, it flies haphazardly about the stage, jumping between foreground and background in an unpredictable fashion. Whenever it passes the battlefield, it leaves a star which can be used against it - a single blow from any of Kirby's attacks will finish it off. After several passes, the API will pause on the battlefield, releasing a star from either side; this is the best opportunity to land the final blow.
Once the API is defeated, it flies uncontrollably about the area, crashing into pillars, then explodes in a flashy manner. Kirby then does his victory dance and progresses onward to the next level.
Holo Defense API appears in its 2.0 form in Meta Knightmare Returns. The battles remain the same, but with increased attack power and speed. The "Holo" bosses appear in a purple tinge instead of green, and the bosses themselves have appearances based on their upgraded forms from previous games, with the exception of Ice Dragon, which had never previously had an upgraded form, so its appearance in this form is entirely new. Holo-Coily Rattler's head appears red. The crystals themselves gain extra points on their sides, rather than being simple diamond shapes as before.
This hologram was created by analyzing data of the cloud monster who is believed to have inhabited the sky of this planet since ancient times. It excels at electrical attacks charged by the atmosphere.”
"API" stands for "Application Programming Interface".
From a gameplay perspective, Holo Defense API is similar to Adeleine; both of them draw/summon previous bosses to battle, and only take one hit to defeat when they're attacking Kirby themselves.
Both also summon the Ice Dragon and Kracko as opponents. However, the former uses Kracko as their final creation during her fight in Kirby's Dream Land 3, while the latter opens the battle with their replica of Kracko.
Holo Defense API closely resembles Pix, the boss of Rock Star in Kirby 64: The Crystal Shards. Both are technological bosses resembling multiple floating crystals, which shatter and leave only their wire frames after being defeated. In addition, they are also the second bosses to be fought in both games overall.
This is because, after Susie's disappearance, President Haltmann gained access to numerous worlds to travel to, allowing him to collect the data (presumably from Rock Star).
The colors of the crystals represent what boss they summon.
The VS. Boss text for the Holo-Doomers refers to the original Sphere Doomers as red and blue, when the regular Sphere Doomer is actually colored purple.
The Holo-Bosses summoned by Holo Defense API 2.0 are altered to resemble their upgraded counterparts from previous appearances:
Holo-Kracko 2.0 resembles Kracko's Revenge from Kirby Super Star Ultra.
Holo-Doomers 2.0 resembles the Sphere Doomers EX from Kirby's Return to Dream Land.