What is wrong with my keydown script?

Let's start with the error message. It gives you a clue on what's going on. In case if you didn't know, eof means end of file, or basically the end of the script.

So basically we're missing some ends! This would've been avoided if you tabbed your code correctly.

bin = script.Parent

me = script.Parent.Parent.Parent
--[[
	or
	local Player = game.Players.LocalPlayer
	local Character = Player.Character or Player.CharacterAdded:wait()
--]]

local enabled = true
local bin = script.Parent

bin.Selected:connect(function(mouse)
	mouse.KeyDown:connect(function(key)
		if key == "c" then
			if enabled == false then
				return
			end
			enabled = false
			me.Character.Torso.Anchored = true
			RightShoulder = me.Character.Torso["Right Shoulder"]
			RightShoulder.C0 = RightShoulder.C0*CFrame.Angles(-0.1,0,0)
			wait(0.1)
			RightShoulder.C0 = RightShoulder.C0*CFrame.Angles(-0.2,0,0)
			wait(0.1)
			RightShoulder.C0 = RightShoulder.C0*CFrame.Angles(-0.3,0,0)
			wait(0.1)
			RightShoulder.C0 = RightShoulder.C0*CFrame.Angles(-0.4,0,0)
			wait(0.1)
			RightShoulder.C0 = RightShoulder.C0*CFrame.Angles(-0.5,0,0)
			wait(0.1)
			game:GetService("Chat"):Chat(me.Character.Head, "Survey the Heavens, Open the Heavens...")
			wait(0.5)
			game:GetService("Chat"):Chat(me.Character.Head, "Oh 88 Stars of the heaven...")
			wait(0.1)
			game:GetService("Chat"):Chat(me.Character.Head, "Shine!")
			wait(0.1)
			game:GetService("Chat"):Chat(me.Character.Head, "Urano Metria!")
			wait(0.1)
			local model = bin.Monster:clone() 
			me.Character.Humanoid.Name = "Me"
			model.Parent = me.Character
			model:MakeJoints()
			model.Gemini.Torso.CFrame = me.Character.Torso.CFrame * CFrame.new(9,0,0)
			model.Gemini.Follow.Disabled = false
			LeftShoulder = model.Gemini.Torso["Left Shoulder"]
			LeftShoulder.C0 = LeftShoulder.C0*CFrame.Angles(0.1,0,0)
			wait(0.1)
			LeftShoulder.C0 = LeftShoulder.C0*CFrame.Angles(0.2,0,0)
			wait(0.1)
			LeftShoulder.C0 = LeftShoulder.C0*CFrame.Angles(0.3,0,0)
			wait(0.1)
			LeftShoulder.C0 = LeftShoulder.C0*CFrame.Angles(0.4,0,0)
			wait(0.1)
			LeftShoulder.C0 = LeftShoulder.C0*CFrame.Angles(0.5,0,0)
			wait(0.1)
			MagicSym = Instance.new("Part")
			MagicSym.Parent = me.Character.Torso
			MagicSym.Anchored = true
			MagicSym.CanCollide = false
			MagicSym.formFactor = "Symmetric"
			MagicSym.BrickColor = BrickColor.new("New Yeller")
			MagicSym.Transparency = 1
			MagicSym.Name = "MagicSym"
			MagicSym.Size = Vector3.new(30, 1, 30)
			MagicSym.TopSurface = "Smooth"
			MagicSym.CFrame = me.Character.Torso.CFrame*CFrame.new(4.5,-3, 0)
			d = Instance.new("Decal")
			d.Name = "Circle"
			d.Parent = MagicSym
			d.Face = "Top"
			d.Texture = "http://www.roblox.com/asset/?id=214848393"
			for loop = 1, 200 do
				MagicSym.CFrame = MagicSym.CFrame *CFrame.Angles(0, 0.005, 0)
				wait(1/25)
			end
			wait(3)
			MagicSym:Destroy() -- Don't use :Remove()!
			me.Character.Torso.Anchored = false
			RightShoulder = me.Character.Torso["Right Shoulder"]
			RightShoulder.C0 = RightShoulder.C0*CFrame.Angles(0.4,0,0)
			RightShoulder.C0 = RightShoulder.C0*CFrame.Angles(0.3,0,0)
			RightShoulder.C0 = RightShoulder.C0*CFrame.Angles(0.2,0,0)
			RightShoulder.C0 = RightShoulder.C0*CFrame.Angles(0.1,0,0)
			RightShoulder.C0 = RightShoulder.C0*CFrame.Angles(0,0,0)
			RightShoulder.C0 = RightShoulder.C0*CFrame.Angles(0.5,0,0)
			if me.Character:FindFirstChild("Monster")~= nil then    
				game:GetService("Chat"):Chat(me.Character.Head, "Thank you!")
				model:Destroy() -- Don't use :Remove()!
				me.Character.Me.Name = "Humanoid"
            else
            end
			if me.Character:FindFirstChild("Me")~= nil then
				me.Character.Me.Name = "Humanoid"
			else
			end
			wait()
	
			enabled = true
			mouse.Icon = "rbxasset://textures\\GunCursor.png"
		end
-- We're missing 2 ends here.

function onSelected(mouse)
	mouse.Icon = "rbxasset://textures\\GunCursor.png"
	mouse.Button1Down:connect(function() onButton1Down(mouse) end)
	-- There's no such function as "onButton1Down()"
end

bin.Selected:connect(onSelected)
end -- This is not needed. You're not really closing anything.

If you want to further improve your script, please look into...

Local variables

:Destroy() method

UserInputService