Sunnycide is an egg-like Shroob monster that was created during the Shroob invasion of the Mushroom Kingdom in Mario & Luigi: Partners in Time, in case something went wrong with their plan of preventing the Yoshis from helping the Mushroom Kingdom. This strange monster was stationed inside Yoob's belly, where it served as the guardian of the Shroob-created eggs holding the captured Yoshis. Sunnycide would watch over these eggs until they presumably hatched and became more monstrous Yoobs to conquer Yoshi's Island. Sunnycide also guarded the exit to Yoob's stomach, preventing anyone from leaving the intestinal factory. At last, Sunnycide was destroyed by the four Mario Brothers of past and present (Mario, Luigi, Baby Mario, Baby Luigi).
Sunnycide resembles a large pink egg with green spots (similar to Yoob's egg). The shell is cracked through the middle horizontally, creating a mouth and separating Sunnycide's body into two halves. Two eyestalks sprout from the top of the egg, while two tentacle-like arms and two round feet emerge from the bottom half. Inside the mouth is Sunnycide's weak spot, a large bump complete with a bandage.
After the Mario brothers helped a band of Yoshis through the factory in Yoob's stomach, the heroes eventually entered the lair of Sunnycide. The monstrous egg creature immediately attacked the Mario Bros, beginning the inevitable battle. Luigi kept trying to run away but repeatedly was blocked. During the confrontation, Sunnycide's primary attack was picking up the Yoob eggs resting in his lair and flinging them at a Mario brother, using a targeting reticule similar to Yoshi's when he throws a Yoshi egg. The Mario brothers could Jump over the eggs to dodge the attack. When the monster ran out of eggs, Sunnycide would slam the ground and five more eggs would fall from the ceiling. Sunnycide would also attempt to inhale a Mario Bro. and eat him. As the Bro. moved closer, the corresponding Baby Bro. could use his Hammer to strike Sunnycide's weak point inside its mouth, thus countering the attack. If the brother was eaten, Sunnycide would recover some HP and the Mario Bro. would inexplicably fall from the ceiling, injuring himself in the process.
Since Sunnycide was encased in a hard, outer shell, most attacks were useless against the egg monster, although it suffered from a weakness against fire. To defeat Sunnycide, the Mario Bros. had to find a way to attack the monster's weak spot inside its mouth. To do this, Mario and Luigi broke open the Shroob eggs used by Sunnycide as weapons and freed the Yoshis trapped inside. After a Yoshi was freed, it would run up to a ledge overlooking the battlefield and attempt to aid the Mario brothers by pushing a large Chomp Rock on top of Sunnycide. Unfortunately, one Yoshi was not strong enough to push the Chomp Rock off the ledge. Five Yoshis were needed to push the Chomp Rock onto Sunnycide. Incidentally, every set of five Yoshis had one green Yoshi, one black Yoshi, one blue Yoshi, one light blue Yoshi, and one pink Yoshi.
After the five Yoshis pushed the Chomp Rock off the ledge, the huge stone would knock Sunnycide on its back, exposing its weak point (the Yoshis would then run off to safety instead of staying and fighting). Hoewever Sunnycide was not finished attacking the brothers yet. While on its back, Sunnycide could perform two moves. First, Sunnycide could pull a chain, creating a hole in the floor. To dodge this attack, Mario or Luigi had to jump right before the hole appeared. The hole would quickly disappear, allowing the Mario brother to fall on solid ground. If the Bro. fell through the hole, he would again inexplicably fall from the ceiling and hit the floor, getting damaged in the process. Additionally, Sunnycide could pull a rope that turned out the lights in Yoob's stomach. This technique would also summon a Boo to attack either Mario or Luigi. Although dim, the Boo could still be easily seen, allowing the Baby Bro. to block the ghost's attack with a Hammer strike. The level of the chain or rope corresponded to the level each Bro was standing on. They could find the Bro he was attacking by looking at which arms he was using to pull it. His right hand goes to Mario and his left goes to Luigi.
Eventually, Sunnycide would manage to get back up and continue throwing eggs at the four Mario brothers. Thus the brothers freed more Yoshis to knock Sunnycide back down. After repeated attacks, Sunnycide exploded in a brilliant fashion and any remaining eggs broke open, releasing the Yoshis trapped inside (that would promptly run away). With the egg guardian destroyed, the freed Yoshis, the four Mario brothers, the captured Toadbert, and the previously imprisoned Baby Bowser escaped through Yoob's intestines back to the safety of Yoshi's Island.
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