Particles

How can i spawn a particle behind a player?

Do you want to spawn them when the player moves, or all the time?

Same. You can't move a particle. You can only spawn new ones.

spawn them

Read carefully! "When the player moves"

You could make a repeating task instead of when the player moves. It may lag depending on how fast or how many you spawn.

PHP:

$level->addParticle($particle, $players);