Attempt to index local 'player' (a nil value)?

A character isn't going to be the only thing that is added to the Workspace. An easy way to fix this is to add an if statement that checks to see if the character is actually a character.

game.Workspace.ChildAdded:connect(function(char)
    if game.Players:GetPlayerFromCharacter(char) then
        local player = game.Players:GetPlayerFromCharacter(char)
        local stats = player.leaderstats
        local spawn = game.Workspace:FindFirstChild(stats.Level.Value)
        char.Torso.CFrame = char.Torso.CFrame + Vector3.new(0,3,0)
        wait()
        char.Torso.CFrame = spawn.CFrame + Vector3.new(0,3,0)
    end
end)

`