I assume you’re using a decal for this. When you have a decal, there may possibly be transparent edges on the sides. Make sure that when you made your decal it’s smooth and flows together. You could also try what Incapaxx said, as that would be much easier!
game:GetService("UserInputService").InputBegan:Connect(function(key)
local player = game.Players.LocalPlayer
local char = player.Character
if key.KeyCode == Enum.KeyCode.F then
local trail = script:FindFirstChild("Trail"):Clone()
trail.Parent = char.Head
local attachment0 = Instance.new("Attachment",char.Head)
attachment0.Name = "TrailAttachment0"
local attachment1 = Instance.new("Attachment",char.HumanoidRootPart)
attachment1.Name = "TrailAttachment1"
trail.Attachment0 = attachment0
trail.Attachment1 = attachment1
end
if key.KeyCode == Enum.KeyCode.V then
char.HumanoidRootPart:WaitForChild('TrailAttachment1'):Destroy()
end
end)
There’s nothing wrong with your script, but if you want the trail to look like lightning then you’re going to need a texture which also fits that description. Basically all you need to do is find a texture with a bunch of lines (or make one yourself) and then put that on the trail. After that, follow @Dudeguy90539 's instructions and your trail will look almost identical to the one that you are trying to replicate.
I don’t think it can be explained any simpler than creating your own texture or adding several smaller trails to your character’s limbs with more attachments. Replicate what you currently have en masse by creating more sets of attachments and trails in player limbs and then just iterate over them to enable or disable them.