Bullet Seed (タネマシンガン Seed Machine Gun) is Ivysaur's neutral special move. With this move, Ivysaur will send a barrage of seeds ascending from its bulb, inflicting 40%-50% damage to foes trapped within the assault. Any opponents to Ivysaur's immediate left and right hit by the animation will get launched into the stream of seeds, making the move even more effective with its hidden small horizontal range. The special attack button can be held to continuously shoot seeds, but the maximum is 5 seconds (similar to the actual Pokémon games, where it can only hit up to five times). The sheer damage and the opponent being caught in the air offers Ivysaur's powerful up-smash as a follow up move to knock the opponent off the screen.
Interestingly, Bullet Seed actually does more damage if the opponent isn't struck by the initial shockwave, keeping them much closer to Ivysaur. Over 70% damage can be dealt this way.
 Description from the Instruction Booklet
Attack by launching tiny seeds upwards in a rapid machine-gun-like fashion.
Bullet Seed is a Special Grass-type attack that was introduced in Generation III from the Pokémon series. It has no outside-of-battle effects. In battle, Bullet Seed is a weak attack, only having 10 base power for each hit in Generations III and IV, and 25 base power for each hit in Generation V. However, Bullet Seed can hit two to five times for each time the move is used. There is a 37.5% chance of Bullet Seed hitting two times or three times, and a 12.5% chance of it hitting four times or five times. It is often learned at low levels by wild Grass-type Pokémon.