Brug Mass

Unidentified Life Form 27 is a large, purple beast with tentacles. It is made up of many smaller purple-colored bugs.

The Battle
ULF 27 is the first boss battle in Metroid: Other M. Shortly after encountering the dead corpse of a scientist (whose lab coat is covered in green blood), a purple bug crawls out from under it, later killed by Lyle. As Samus Aran, who was accompanying the group, starts to talk to Adam Malkovich about letting her on the team, several more purple bugs crawl down the walls and ceiling, forming into the beast.

Initially, the Marines and Samus are unable to destroy it. However, they hatch a plan: Samus must fire a Charge Beam shot into the creature's single eye, allowing the Marines use their Freeze Guns to freeze up the tentacles of the beast to allow Samus to fire a Missile to destroy the arm. Once the arms have been destroyed, the base of the creature becomes vulnerable to attack. In this form, the creature slams its whole body into the ground in an attempt to injure Samus or one of the Marines. After the base has been destroyed, Samus must attack its eye to finish off the beast. During the fight, Adam Malkovich authorizes the troopers to use ice weaponry, and Samus to use Missiles. The fight also earns Samus the respect of Malkovich once again.

Trivia

 * Unidentified Life Form 27 was referred to as such in UK's Official Nintendo Magazine: "An early encounter with a giant one-eyed monster (Unidentified Life Form 27)".
 * The fact that the creature is made up of smaller bugs makes it similar to the Shadow Bugs in Super Smash Bros. Brawl.
 * If one thinks about it, Samus could've used the Seeker Missle to destroy the monster much faster, most likely without the other Federation Troops. (There are five spots including the monsters giant eye)