i need help making a custom weapon

...Good luck? You're probably going to have to code a similar behavior from scratch.

I'd recommend doing something with the player's look angle vector to get the entity or block they're targeting, then generating the particles along said vector, and running an entity iterator to do magic damage at the target location. ...It's not exactly like the warden's beam, but there's not really a way to replicate it for players. The Warden's attack literally just locks onto a nearby player and damages them, it only generates the particles as an afterthought, to make it look like a beam- that's how it cuts through walls, and why you can't easily avoid it once the warden's locked on.

You can certainly make something similar, but it may be more trouble than it's worth.