but I am messing up every time I try to make something like that what kind of decal should I use to make a trail like that? should the decal be long? like a circle which has trail instead of circle? or what should I make so that my Trail looks like that
I think what you need first is a decal that has a background transparency. then add some random splashes to it.
I believe the easiest method would be to set it to a texture of a trail. Then make the texture length something quite long. So when the trail plays the background should be transparent.(I am not sure of how to do that but I am sure someone out there does.
Then in a script you just either need to start the trail at the start of the animation track playing or add some animation events e.g. SwingStart, SwingEnd, Preparation (You can also put a delay on it and manually line it up) Then stop it once the swing ends.
This is just a demo of what such a script could look like
-- Prerequisites: Already loaded and playing animation
local SwingFinishedSignal = AnimationTrack:GetMarkerReachedSignal ("SwingEnd")
local SwingStartConnection = AnimationTrack:GetMarkerReachedSignal("SwingStart"):Connect(function()
Sword.Effects.SwordTrail.Enabled = true
SwingFinishedSignal:Wait() -- This will yield forever if the animation is cancelled mid swing.
Sword.Effects.SwordTrail.Enabled = false
end)