Kretin (known as Keratin in the PAL release) is a molecule with two forms called Alpha Kretin and Beta Kretin (Alpha Keratin and Beta Keratin in the PAL release) who, in Mario & Luigi: Bowser's Inside Story, kidnaps Princess Peach. After a long chase in the Flab Zone, Mario & Luigi finally reached Kretin. Using the spin move, Mario and Luigi free Peach from the grips of it, but immediately get attacked by Kretin.
In battle, Kretin will begin in its Alpha Kretin form. Each individual unit of Kretin can be either red or green, and can only be damaged by the Mario brother of the corresponding color. When one unit receives enough damage, it turns blue and is defeated. After all the six parts of Kretin are blue, it will falll apart. Five units disappear, but one remains. It will proceed to create five clones in a hexagon pattern. These clones are very weak and are defeated in a single attack. If a duplicate is defeated, the real Kretin will simply create another on the next turn. Creating a new clone does take up a full turn; Kretin can recreate the duplicate and attack in the same turn.
The Alpha Kretin's only attack is creating a ball of blue electric energy that will move through its body. It will then start to glow, turning its arm into a cannon shape. The Alpha Kretin will start to shoot balls of energy towards the Bros. The player can know which Bro. the ball will go toward by the order the beam went through the body, red for Mario, green for Luigi, nothing for blue. This means that the more Kretins defeated, the less balls Alpha Kretin can shoot. This attack is countered with hammers. If hit the, Bros. can get a DEF-Down. In its Beta Kretin form, it will create five duplicates of itself and start to jump around, trying to confuse the player by jumping to a different position. If a fake Beta Kretin is defeated, the real one will just create another copy. Its main attack is surrounding the bros in a hexagon shape. They will all start to charge up electricity. When one of the Kretins jumps, that's where the electricity will move on to. This attack can be avoided by jumping. After the fight, Kretin is defeated. A stronger version of Kretin can be fought in The Gauntlet, this form is known as Kretin X.
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