Decoding Encoded base64 string using MSIL

$test = @"
using System;
using System.Text;
using System.Reflection;
using System.Reflection.Emit;
using System.Globalization;
public class Wrapper {
    // Declare a delegate type that can be used to execute the completed dynamic method.
    private delegate string BaseDelegate(string input);

    public static void WOW(string input)
    {
        // Create a dynamic method with the name "Base", a return type of string, and one string parameter
        DynamicMethod baseDM = new DynamicMethod("Base",typeof(string),new Type[] { typeof(string) }, typeof(string).Module);

        MethodInfo base64Convertor = typeof(System.Convert).GetMethods()[308]; // System.Convert.FromBase64String
        MethodInfo getUTF8Encoding = typeof(System.Text.Encoding).GetMethod("get_UTF8", new Type[] { });
        MethodInfo getString = System.Text.Encoding.UTF8.GetType().GetMethod("GetString", new Type[] { typeof(byte[]) });

        ILGenerator il = baseDM.GetILGenerator(512);
        // Get UTF8 object
        il.EmitCall(OpCodes.Call, getUTF8Encoding, null);
        // Load the first argument, which is a string, onto the stack.
        il.Emit(OpCodes.Ldarg_0);
        // Call Convert.FromBase64String
        il.EmitCall(OpCodes.Call, base64Convertor, null);
        // Call UTF8.GetString
        il.EmitCall(OpCodes.Callvirt, getString, null);
        // Return the top value on the evaluation stack
        il.Emit(OpCodes.Ret);

        // Create a delegate that represents the dynamic method. This
        // action completes the method. Any further attempts to
        // change the method are ignored.
        BaseDelegate bbb = (BaseDelegate)baseDM.CreateDelegate(typeof(BaseDelegate));

        var ccc= bbb(input);
        Console.WriteLine(ccc);

    }
}
"@

Add-Type -TypeDefinition $test

[Wrapper]::WOW("dGhpcyBpcyBhIHRlc3Q=")