Script works in studio, but when i enter game it's doesn't work. In DevConsole "c it's nil value". ?

Are you using LocalScript or Script? If Script, So it should be in LocalScript.

LocalPlayer and GetMouse is client side only.

Edit:

Try this.

repeat wait() until game.Players.LocalPlayer
repeat wait() until game.Players.LocalPlayer.Character  
player = game.Players.LocalPlayer 
mouse = player:GetMouse() 
c = player.Character 
anima = script:WaitForChild("Smash") 
Enabled = true 

mouse.KeyDown:connect(function(key)
    key = key:lower()
    if key == "z" then
        if not Enabled then return end
        Enabled = false
        local AnimaStart = c.Humanoid:LoadAnimation(anima)
        AnimaStart:Play()
        c.Humanoid.Health = c.Humanoid.Health -15
        local q = Instance.new("Part", c)
        q.Shape = "Block"
        q.Anchored = true
        q.CanCollide = false
        q.BottomSurface = "Smooth"
        q.TopSurface = "Smooth"
        q.Material = "Metal"
        q.Transparency = 0.3
        q.BrickColor = BrickColor.new("Ghost grey")
        q.Size = Vector3.new(5,5,25)
        q.CFrame = c.Torso.CFrame *CFrame.new(1.3,0,-15)
        local u = Instance.new("SpecialMesh")
        u.MeshType = "Sphere"
        u.Parent = q

        for i = 1, 20 do
            q.Size = q.Size +Vector3.new(1,1,1)
            wait()
            q.Transparency = q.Transparency +0.1
            q.Size = q.Size +Vector3.new(1,1,1)
            wait()
            q.Transparency = q.Transparency +0.1
            q.Size = q.Size +Vector3.new(1,1,1)
            wait()
            q.Transparency = q.Transparency +0.1
            q.Size = q.Size +Vector3.new(0,0,0.1)
            wait()
        end
    wait(5)
    q:Destroy()
    Enabled = true
    end
end)