Double Team

Double Team is Lucario's Down Special Move. When used, Lucario enters a defensive tai chi-like stance. If it is attacked during this stance, it will teleport behind the attacker, then strike with a sliding kick for moderate damage and surprisingly high knockback, which is even greater after Lucario has taken damage. If Lucario successfully counters with Double Team near an edge, it may teleport above the ledge and fall downwards as it unsuccessfully attacks, making recovery difficult. There is some kind of lag after doing the attack in midair. Double Team has a shorter length than Marth's and Ike's Counter, but does more damage and knockback if it is pulled off. In fact, Double Team is the strongest counterattack in the game. One of the most interesting features of Double Team is its damageable area elimination. If Lucario is hit during a Double Team and goes into the counter strike, Lucario will not have a damageable area until it completes the counter attack. Lucario can't be hit, grabbed, or even caught in a Final Smash by anyone or anything. Double Team also reduces Lucario's falling speed for a minor duration. This move is rather easy to dodge, as it is possible to air dodge or shield the attack when Lucario disappears. It also has some invincibility frames to it when activated. Initial damage is 7% and at 165%(where it caps) is 15%.

Note that Lucario actually strikes the location around where it was hit, just like Counter does. If Double Team is used on a ranged attack, or an attack that causes its user to move quickly (Spin Dash, Rollout, etc.), Lucario will most likely miss with his counter attack.

Origin
In the Pokémon games, Double Team is a Normal-type move which raises evasion, making attacks miss more often, and can be stacked for even larger evasion boosts. It is generally banned in competitive play for its reliance on luck and its difficulty to counter effectively when paired with Baton Pass. The animation in Brawl is similar to the animation in the Pokémon games (notably ones like Pokémon Battle Revolution or Pokémon Colosseum).

Trivia

 * It is possible to pull off a "reverse" Double Team where Lucario attacks from the front. After using Double Team, simply hold the joystick in the direction you wish to attack from. Advantages of pulling off a "reverse" Double Team include allowing Lucario to initiate combos and even wall-cling without the use of a second jump. Video can be seen here.
 * With precise timing, Lucario's Double Team can activate Marth's Counter.
 * With precise timing, Lucario can also dodge some Final Smashes. Some of the dodgeable smashes are Pikachu's Volt Tackle, Pit's Palutena's Army, Ice Climbers's Iceberg (You will take some damage.), Lucas and Ness' PK Starstorm.
 * In the Pokémon games, Double Team deals no damage, instead making the user much harder to hit, but the animation is largely the same as the attack in Brawl.
 * Double Team does not work for some Final Smashes, but against all regular attacks(ground and aerial) and special attacks.
 * Lucario quietly says "It's over" whenever Double Team is successfully activated, but this phrase is barely recognizable by many players due to many other sound effects and music unless one plays the game in high-definition volume settings. Regardless, this phrase is available in the "Sound Room."
 * If Lucario uses Double Team with a Pikmin attached to it and attacking, the Pikmin will "vanish" with Lucario.
 * If you use Double Team in Pokemon Stadium 2 while riding the treadmill (in the stage's Electric field) until you fall off, you will float.