Meta Knight perfecting shielding Samus's missile.
A perfect shield, also refered to as power shielding or power shield, is both an effect and a technique in Super Smash Flash 2.
Because a normal shield is a bubble of energy that starts to dwindle in size and weaken the instant it starts, it is the strongest at the very first frame the shield is activated. This first frame of the shield is the "perfect shield".
When a hitbox projectile, disjointed, melee or otherwise hits a perfect shield the entire screen will flash white for a brief split second, followed by a pinging sound that vaugely resembles a "ding".
Perfect shields prevents a shielding character from being knocked backwards, and the attack that was perfectly blocked will not reduce in size due to the attack itself. If the hitbox in question is a projectile, a perfect shield can reflect most of them. Unless the opponent whose projectiles were reflected was a long distance away, or has invincibility frames, the projectiles are usually reflected very quickly, much quicker than the projectile's normal speed. (Goku's ki blasts, when perfect shielded, will reflect with more than three times the projectile's normal speed. The same applies for Naruto's Shadow Clone Toss as well as several unnamed others.)
Some other projectiles are way too powerful to be reflected by even a perfect shield. Instead, they cause a small aura to explode out from the shield as the projectile hits it. It can hit enemies who are close by with the same strength as the "reflected" projectile, but the projectile itself will continue on its normal path. Ironically, a normal shield would absorb most of these more powerful projectiles.
There are several more unique reflection properties of perfect shields. Black Mage's fully charged forward smash is a small patch of lightning which sweeps the entire stage, striking every two or so seconds. If someone perfect shields the lightning strike, the attack would go the opposite way, still strifing the ground normally.
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