When used, Piranha Plant hides back into its pot/pipe. When the button is released, Piranha Plant shoots out and bites viciously - the longer the charge, the farther Piranha Plant reaches.
The pot has 15% damage-based armor during the attack from frame 9 until shortly after the release, and a direction can be inputted to turn Piranha Plant left or right. Upon release, this reduces to 12%. It also has a 0.8× damage multiplier, which does affect KO percentages. The new damage scales with the 1v1 multiplier last, meaning 10% base damage will reduce to 8% first, and then be multiplied up to 9.6%. The 1v1 multiplier, as usual, does not affect KO percentages itself. This means that the halved damage before being multiplied will be what is used in knockback calculation. Overall, Long-Stem Strike has valid use for survivability and edgeguarding purposes.
However, one must be careful when turning before the strike, as the pot/pipe cannot change directions after an initial input. If it lies on its side the attack is stuck at a specific angle, making it easier to dodge. It can also get stuck on the ground if tilted too much in the air, leaving the character wide open to attack or grabs. Knowing how to control this is essential to the move's success.
Upon release, Piranha Plant possesses a proximity detection hitbox that will trigger the attack as soon as an opponent is reached, but it can be started early via pushing the special button. However, the difference is negligible offensively and is largely used for mixups and fake-outs. The attack itself possesses intangibility on the head from frames 1-6, allowing it to go through projectiles. It also deals 5 HP bonus damage to shields, making it useful for shield breaks. Piranha Plant's hurtbox is, however, expanded during the attack, and any knockback taken will start momentum from the pot/pipe. Due to this, it is possible to meteor smash Piranha Plant from very far away.
Strike Cancel Glitch
Prior to 4.0.0, Piranha Plant had a glitch with Long-Stem Strike that would replace the Bite animation with Ptooie's Swallow animation. To perform this, Piranha Plant would have to get hit by an opponent's attack a frame before, or on the frame, that Ptooie would be swallowed. Then, if Long-Stem Strike were to be used and slightly tilted, the Bite animation would instead come out as the Swallow animation, removing the hitboxes, intangibility and essentially any reference of the bite attack completely. The tech had very little utility due to the arduous process of managing to fulfill the conditions, but it did find its way into battles by chance.
This is a reference to the Stalking Piranha Plants that first appeared in New Super Mario Bros. Wii. When they are encountered, the height of their stem changes sporadically, making it hard for the player to jump past.