Megabug

MegaBug, (also referred to as the MegaDragon and later MegaDragonBowser after merging with Bowser) is the main antagonist in Mario + Rabbids: Kingdom Battle. It is an evil virus accidentally created by the Rabbids and now seeks to erase the Mario and Rabbids universe.

Biography
While little is specifically known about the MegaBug, it seems to be the very reason why everything bad is happening, and that whenever the heroes defeat a foe corrupted by its energy, the MegaBug comes closer to its main goal; destroy and consume everything in the world. When it possesses Bowser, Bowser Jr., the former primary antagonist, shows honor and begs the heroes to save his dad.

Every time the heroes defeat a hostile Rabbid, the MegaBug grows slightly, as it absorbs its energy that corrupted the Rabbid in the first place. However, it is required to defeat hostile Rabbids as they endanger the Mushroom Kingdom. It is clear from this that the MegaBug engineered the situation for Mario and company to fail, apparently proving that despite being mute, it is a very clever creature that can engineer situations to its own advantage.

By the time Mario and his friends recover Spawny from the Lava Pits, the MegaBug has attained enough energy from the Rabbids to manifest a physical form. It grabs Spawny, acquiring his merging ability, and creates a multitude of minions (including Bwario, Bwaluigi, and the Lava Queen) to stall its enemies' progress as it finds a powerful life-force to gain unlimited strength, in this case Bowser.

During its boss battle as MegaDragonBowser, it uses minions to battle on its behalf, but will occasionally launch an attack itself as well, even if it means harming its own minions. However, whenever it spins in it's shell, it becomes defenseless and vulnerable.

After getting defeated, the MegaBug separates from Bowser and makes one last ditch effort to kill the heroes once and for all, but Mario's team fire a series of blasts at the beast, destroying it for good and returning the Mushroom Kingdom back to normal.

Physical description
The MegaBug has two forms that he shifts between.

While in his regular form, The MegaBug looks very strange, possessing yellow-brown-red molten wings and a small head with the same color.

When he is fused with Bowser, the MegaBug becomes the "Mega Dragon Bowser", and he now has a molten pattern on his body along with red eyes, though he keeps the red wings.

Megabug
As the MegaBug, it is a neon-bright and paper-thin creature with a shiny, long serpent-like body, very bright yellow eyes, a swirly tail, and two large wings that is bigger than the rest of its yellow, red, and orange colored body. Its wingtips are also pixelated.

MegaDragonBowser
When Bowser comes home from vacation early, the MegaBug does something to him that leaves him dazed. It then possesses his body to increase its own strength further, which results in the two merging into MegaDragonBowser.

This form retains most of Bowser's normal appearance, but it also applies features of the MegaBug. This includes orange patterns glowing on its body, extremely bright yellow eyes, long curly tail, and large wings that enables it flight. Overall, MegaDragonBowser resembles a demonic Phoenix/Dragon-like version of Bowser.

Powers and Abilities
By itself, the only abilities the MegaBug is shown to have is flight and body possession. However, since it has absorbed much of its energy prior to its confrontation with the heroes, the MegaBug is assumed to be quite strong and powerful in its own right. It managed to daze Bowser long enough to possess him and even after the MegaBug was weakened from its battle as MegaDragonBowser, it was only bought down by a barrage of energy blasts fired by the heroes.

While the MegaBug alone is seen as a very weak and skinny creature that won't ever win a fight by himself, as seen after he is done possessing Bowser and he doesn't have a fighting chance against Mario and his friends, it is basically capable of doing everything because of being able to possess people, and in addition, he can also fly, which is an advantage when possessing.

After fusing with Bowser, it becomes extremely powerful, with the ability to fly, along with Bowser's other skills, such as shell-spinning and fire breathing.

After fusing with Bowser, the MegaBug becomes even more powerful. It obtains (and possibly enchants) all of Bowser abilities, while also keeping its own ability to fly, making it a very dangerous foe.

Mario + Rabbids Kingdom Battle
MegaBug appears as the final boss of Mario + Rabbids Kingdom Battle.

Battle
The MegaDragonBowser has three phases and 4,800 hit points. During the first phase, it will be surrounded by four infernal Valkyries. His attacks include the following:


 * 1) Taking flight and attacking one character with a stream of small fireballs from his hand, similar to a Rumblebang; these shots can destroy Mega Blocks and inflict the Burn status.
 * 2) Activating a line-of-sight technique that allows him to shoot a character if they move between his turns.
 * 3) Drawing characters towards him, similar to Rabbid Mario's Magnet Dance.
 * 4) Slamming onto the ground, creating a shockwave that damages and blows back anyone in range. Destroys Mega Blocks in range as well.

After it has two-thirds his total health bar, MegaDragonBowser enters phase two and takes to the air. it immediately bombards the battlefield with fireballs, inflicting 20 HP damage and a Burn on any characters in their path and leaving scorched craters where they land. After summoning four Lava Bucklers near the middle of the arena, it will spend the rest of this phase flying around the sides of the battlefield and raining fireballs on the craters, as well as using a protection technique to reduce damage to his minions by taking a fraction of the damage himself. The heroes must attack MegaDragonBowser to deplete his HP again, but dealing with the Bucklers first is highly advised.

Once it is down to its final third of itsstamina, MegaDragonBowser enters phase three. MegaDragonBowser returns to the arena (being once again vulnerable to line-of-sight attacks while he moves) and uses his melee smash on the center as he lands. As four Lava Smashers spawn around him, he now attacks with Whirling Fortress and shields himself on the heroes' turn (raising his defense to infinite). To harm the boss, the heroes must lure him into spinning at the metal blocks around the arena - impact with a block will shatter it and stun MegaDragonBowser for a turn.

Once his stamina is fully drained, MegaDragonBowser is defeated. The MegaBug and Bowser separate, and the former attempts one final attack against the heroes to hold onto his control of the kingdom, but the heroes respond with an offensive of their own, allowing them to destroy the aberration... for good.

Trivia

 * Etymology: The MegaBug may have earned his name how he resembles a computer glitch.
 * Despite his small amount of screen time in the game, The MegaBug is one of the most evil Mario Villains ever along with Dimentio and the Luigi's Mansion version of King Boo, as he has a desire to destroy everything and is responsible for everything bad that happened in the game.


 * The MegaBug shares a very notable resemblance to the legendary Pokémon Zygarde.
 * The MegaBug's design also shares similarities to Solaris second form.
 * The MegaBug is arguably one of the most serious and evil threats in the Mario series alongside Dimentio and King Boo, but does not have a clear moral agency despite being taken seriously with their heinous actions, while the Shadow Queen never wanted to cause as much destruction as the MegaBug did, as well as merely following her own nature. In addition, neither Dimentio, King Boo, nor the Shadow Queen killed their minions for kicks, at worst brainwashed them.