A powershield (ジャストシールド, Just shield) (officially called perfect shield in Brawl and SSB4) is a technique where one activates a full shield such that it connects with an incoming attack on the first few frames. In order for the technique to be executed, one must rely on timing and skill. When the opponent is ready to strike, the player must quickly use the shield. If done correctly, the character takes no shield damage (or shieldstun if a projectile was powershielded) and may immediately perform a counterattack while the attacker is stuck in hitlag. The powershield technique in Melee, Brawl and SSB4 is comparable to a parry in traditional fighting games, as it results in little to no knockback and freezes the opponent for a couple frames.
Powershielding is done by quickly and fully depressing a shield button four frames before an attack connects. If done correctly, there will be a significant flash on the shield and a distinctive "chlink" sound. Because it is technically a shield, it is ineffective against grabs. In Melee, powershielding can reflect projectiles during the first two frames, although they deal half their usual damage (unlike other reflectors, which increase their damage), and Poké Balls reflected in this way retain the ownership of the character that threw them. In Brawl and SSB4, powershelding merely redirects projectiles at an angle without changing their ownership.
CPU players, especially level 9s, use this technique a lot to reflect projectiles in Melee and against any incoming attack in Brawl and SSB4. Human players don't use it as much simply because of the reaction times and precision usually required, and as such, it often comes as a surprise and can momentarily disrupt a match. However, it has been made easier in Brawl and SSB4 than in Melee due to the ability to buffer. At high level play, powershielding in Melee can be used to reflect a wave of incoming projectiles such as Falco's laser, to punish camping.
In Melee, the technique is known as power shielding (named for the Power Shielder bonus attained by using the technique multiple times). Power shielding is accomplished by fully pressing L or R such that the shield appears just before the incoming attack would hit you. More specifically, the full shield bubble's inner reflection hitbox must connect with the hitbox of the incoming attack within 4 frames of activating the shield. The noise heard by doing this is rather quiet compared to Brawl's, and should a projectile hit on frames 1 or 2 of the powershield, the technique will reflect projectiles at half the original damage. Though the technique is difficult to perform consistently, powershielding is extremely valuable in competitive play, as it allows players to punish moves with low ending lag such as Fox's neutral aerial. Its ability to reflect projectiles is even more valuable as it allows players to punish otherwise safe, predictable projectile spam, particularly in the Falco matchup, whose lasers can shut off many options and leave a player completely helpless if not dealt with properly.
Though extremely difficult, powershielding projectiles is still humanly possible to perform consistently. Players who use characters with projectiles often have an easily trackable firing pattern, such as firing projectiles only when there is a certain distance between the players. It is also important to note that players (again, Falco mains in particular) will short hop to move while firing. As such, a projectile user running or jumping away from pressure is often a surefire sign they intend to fire. If the projectile is thin like Falco's laser, another thing a player can do to ease the risk and timing needed to powershield is to crouch and wait for the projectile to pass over the character. Shielding while the projectile is directly over the character will ensure a powershielded projectile.
Powershield follow-up is also distance dependent. A laser is considered safe if fired when Falco and his opponent are standing a distance X between each other, where X is the max horizontal distance Falco can jump in 1 short hop. At this distance, powershielding the lasers yield no follow ups and attempting to move around them by jumping, rolling, or going under them with attacks that lower hurtboxes (like Marth's dash attack) put the opponent in positions Falco has an easier time winning neutral in. However, if the laser is fired too far away, for example at distance 1.5X, the laser is not safe, as powershielding does yield follow-ups such as a grab.
Yoshi's shield sometimes powershields attacks even when the shield is already up.
Chronological frame data
By pressing L or R during an actionable grounded frame, the Guard animation will be triggered immediately. The ability to powershield with it depends on whether the button press was digital or analog:
GuardReflect is triggered. Reflecting projectiles is possible during the first two frames. During the first four frames, physical attacks will enable the subsequent cancellation of the GuardOff animation. Both are only possible if the incoming hitbox also overlaps the inner powershield sphere on the first frame of its collision with the shield.
GuardOn is triggered. This animation has no powershield sphere, but the shield sphere is active from the first frame on as well. It can be transitioned to GuardReflect by a digital shoulder button press only on frame one and only if no hitbox collided with the shield on this first frame.
Example of multi-hit attacks that still preserve the physical powershield benefit
Fox stands in front of Marth and does a SHFFL down aerial:
The ability to powershield returns in Brawl, working the same way as in Melee. However, this time, a clear "chlink" sound occurs when executed properly. It is also easier to execute than in Melee, because of the ability to buffer. One major change is that powershielding no longer reflects projectiles; should a projectile connect during powershield frames, they will rebound off the shield at an angle instead of rebounding back towards the owner of the projectile. A projectile that bounces off a character's shield can no longer affect that character unless it's a multi-hit attack.
In Smash 4, powershielding initially worked the exact same way as in Brawl. As of update 1.1.1, however, its action time was reduced from 4 frames to 3 frames, making it more difficult to perform, though this is compensated by powershielding now reducing shieldstun (which has been made much higher by the update) by 25%, making it more rewarding when executed effectively. Powershielding in Smash 4 also produces a quieter sound effect than in Brawl; Ryu is an exception to this, as he instead uses a unique powershield sound effect based on the parry in Street Fighter III.