Today, we will be making a trail for your player with vce. We will be using the critical hit projectile.
33 OnActivate > Self > FireRelay
33 OnRelay > Self > FireRelay
33 OnRelay > player > SpawnProjectile [Critical Hit] [ 0 ] [ 0 ] [ 1 ]
If you're looking for the events for a projectile trail for players, here you go:

Just be cautious with the event, it's really spammy. I'd suggest setting the delay on line 1 to at least 120 milliseconds.
I believe some other variables for player would be <var:pl:firing>, <var:pl:jetting>, <var:pl:crouching>, <var:pl:maxhealth> and <var:pl:jumping>