Shroid

Shroids are grey Shroob robots with yellow spots and green photoreceptors; the name 'Shroid' is actually a portmanteau of the words 'Shroob' and 'droid'. These powerful robots were stationed in Toad Town during the Shroobs' occupation of the Mushroom Kingdom. Shroids patrolled the ruins of the damaged capital city, attacking any intruders. The four Mario Bros. of past and present encountered many Shroids during the heroes' attempt to assemble the Cobalt Star and liberate Toad Town.

In battle, Shroids used a variety of attacks to defeat intruders. First, a Shroid could trap Mario and Luigi in crystals while charging up an energy blast in its arm cannon. The heroic brothers could break these crystal prisons by constantly jumping. After breaking the crystals, one of the brothers would have to jump over the charged energy blast after the Shroid stopped to fire. The brother it shoots at can be predetermined by looking at who it first traps in a crystal. However, if it is malfunctioning, it will shoot at the brother it traps second.

A Shroid could also summon a Shroob UFO to bring a spiked ball to the battlefield. This spiked ball would either have a red "M" or a green "L" printed on it, indicating which Mario Bro. the weapon would be used against. The Shroob UFO would drop the spiked ball on top of the Shroid. The robotic Shroob would then throw the spiked ball at the appropriate Mario Bro. This spiked ball could be deflected with a Hammer strike from one of the Baby Mario Bros. The weapon would then bounce back and hit the Shroid, damaging the robot in the process and causing it to malfunction. If the Shroid is damaged in this way, all future attacks will be reversed. (An attack that should normally hit Mario will hit Luigi instead, and vice versa.)

The Shroid's last technique was less of an attack and more of a test of the Mario brothers' skill. The robotic Shroob would hold up a series of flags: either a red flag, a green flag or both flags each time. Depending on what color the flag is, the corresponding Mario Bro. had to quickly jump (if the Shroid held up both flags, both Mario Bros. had to immediately jump). The Shroid would repeat this process two to six times. If the Bros. messed up (either by missing a jump or by having the wrong Bro. jump), the Shroid would throw both flags at the Mario Bros., damaging them. The flag-throw is undodgeable. If done correctly, the Shroid won't attack. Sometimes, the Shroid would attempt to fake out the heroic brothers, causing the Mario Bros. to jump prematurely (and thus be damaged). Again, if the Shroid is malfunctioning, Luigi should jump if the Shroid holds up the red flag, and vice versa. Both brothers should still jump if the Shroid holds up both flags.

Another type of enemy, the Mecha-Chomp from Mario & Luigi: Superstar Saga, malfunctions in a way similar to a Shroid.

Trivia

 * In Mario & Luigi: Bowser's Inside Story, while Mario and Luigi battle the Shroobs, some Shroids can be seen frozen inside ice blocks.
 * Shroid's name is a portmanteau of "Shroob" and "droid".