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)