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