The Barrier Trio (けっかいトリオ) is a set of enemies in Mother 3. They are purple golem-like creatures created by the Magypsy Mixolydia to guard the Tanetane Island Needle, and are found at the top of the island, on the other end of a cavern past her house.
When examined, it is revealed that their names - "Barrier Man" (けっかいどん), "Barrier Dude" (けっかいくん), and "Barrier Gal" (けっかいちゃん) - are inscribed on their chests. They soon spring to life, starting the battle.
The Barrier Trio's arsenal is composed almost entirely of powerful PK attacks; they can use the β and γ levels of all elemental attacks, and they can bolster their already formidable Defense with Defense Up Ω (even though they are treated as a single enemy). The Trio are also immune to all status ailments. Their battle theme is Strong One, which is fitting for what is likely to be the most difficult boss up to this point, and one that requires more than a fair amount of strategy to win (unless Defense Down is used extensively).
From their first turn, they will immediately strike a Barrier Pose, rendering themselves invulnerable to all but one element of PK for a few turns, based on who calls out the formation (Barrier Man corresponds to fire, Barrier Gal to ice, and Barrier Dude to thunder); their weakness can be confirmed via Boney's Sniff ability. When hit enough, their pose will be crushed, causing them to lose that turn and become vulnerable to other elements until they establish another pose within the next few turns.
Revival items such as Secret Herbs and cups of Lifenoodles, healing methods such as PK Lifeup, and defensive skills such as PSI Shield and PSI Counter are almost required to weather the Barrier Trio's PK assault. Lucas and company must use their strongest available attacks during whatever openings become present; in addition, more damage can be done using Defense Down and Duster's Tickle Stick (since they will focus more on PK attacks if their defense is maxed out).
When the Barrier Trio's HP get low, they will concentrate, signaling that they will use PK Starstorm on the next turn; without a PSI Shield/Counter, regular healing, and well-timed strong attacks, the party will likely perish. The signal for their defeat is when they concentrate again, but lack enough strength to perform another PK Starstorm.
Their battle sound is Battle Sound 60, which is used only by large bosses, falling under Code Numbers 939 for regular attack, 940 for Smaaaash! and 941 for Miss. However, further hacking is required to get them to use their battle sound, as they normally only attack using PSI.
There is a way to defeat the barrier trio more easily, but it is particularly tedious. From the start of the battle, Duster must use his tickle stick and Kumatora must use one of her defense down moves. If the barrier trio's Defense is low enough, it will use Defense Up to replenish its stats rather than attack. By lowering barrier trio's defense each turn, Barrier Trio will constantly be occupied with using Defense Up, giving Lucas and Boney time to chip away at its health. Eventually, Barrier Trio will use PK Starstorm.
Once their HP is completely depleted, the exhausted trio will then perform a now-infamous last action - a final Barrier Pose which the game describes as "spectacular" - before meeting their demise. After their victory, the party attempts to take the Needle, but are preempted by the Pigmask Army. As Lucas and company watch, Pigmasks rush into the area and lay out a red carpet, which signals the arrival of their commander - the Masked Man, who KOs the entire party with a blast of lightning and pulls the Needle.