A perfect shield, also referred to as power shielding, is both a mechanic and a technique in Super Smash Flash 2. The first frame of the shield is the "perfect shield". When a hitbox hits a perfect shield — the first frame of the shield —, a pinging sound will happen. Perfect shields prevent a shielding character from being pushed backwards, and the attack that was perfectly blocked will not cause damage to the shield.
If said is a projectile, a perfect shield may reflect it back at the attacker. Reflected projectiles sometimes travel much quicker than their normal counterparts. Goku's Ki Blasts and Naruto's Shadow Clone Toss are examples of that.
However, some projectiles cannot be reflected at all, and instead will either behave like nothing happened, or will continue along their normal path, while still being able to hit their original owners.