Fireball cant make the fireball to shoot?

Here's a few things, you never want to create instances / do things you want people to see via the client, I'll assist you.

-- >> Client
local UIS = game:GetService("UserInputService")
local Fire = game.ReplicatedStorage.Fire
local Player = game.Players.LocalPlayer    
local Character = Player.Character
local mouse = Player:GetMouse()
local deb = false

UIS.InputBegan:Connect(function(input, isTyping)
	if isTyping then return end
	if input.KeyCode == Enum.KeyCode.E and not deb then
		deb = true
		Fire:FireServer(Mouse.Hit)
		wait(1)
		deb = false
	end
end)

-- >> Server
local Fire = game.ReplicatedStorage.Fire
local deb = false

Fire.OnServerEvent:Connect(function(plrWhoFired, Mouse)
    local char = plrWhoFired.Character or plrWhoFired.CharacterAdded:Wait()

    local Part = Instance.new('Part') -- instancing on the server
    Part.Shape = Enum.PartType.Ball
    Part.CanCollide = false
    Part.Transparency = 0.5
    Part.Parent = workspace
    Part.CFrame = char.HumanoidRootPart.CFrame

    local bodyVelocity = Instance.new("BodyVelocity") -- allows it to shoot
    bodyVelocity.MaxForce = Vector3.new(math.huge, math.huge, math.huge)
    bodyVelocity.Velocity = Mouse.LookVector*30
    bodyVelocity.Parent = Part

    Part.Touched:Connect(function(hit)
        if hit.Parent:FindFirstChild('Humanoid') and hit.Parent.Name ~= plrWhoFired.Name and not deb then -- checks to ensure its a player, and not you
            deb = true
            local otherPlr = hit.Parent.Humanoid
            otherPlr:TakeDamage(50) -- amount you want to damage them
            Part:Destroy()
            wait(1)
            deb = false
		end
	end)
end)