Got the enemies following waypoints now and the towers tracking them. That's enough for tonight! :)

Very cool!  I don't use C# much anymore as I program in C++ 99% of the time, but when you're comparing C++ and C# there will be differences.

For example, if I make a class called enemyOrc: 

orcEnemy myOrc1 = new orcEnemy();

This class is a reference type, so that means if I pass it directly through a function and make changes, it will retain it.

The two confusions that happen is people miss-understand what are reference types, and value types when passing.

I made an example of a class (reference type) and a int (value type) for you.

Also keep in mind, if I'm taking a int health but passing myOrc2.health this is a value type and will not retain the change. I have three examples here:

Passing by reference type

Passing by value type

Passing by value type (from a class variable "myOrc2.health")

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class orcEnemy
    {
        public int health;

        public orcEnemy()
        {
            health = 100;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            orcEnemy myOrc1 = new orcEnemy();
            attackOrc(myOrc1, 25);
            Console.WriteLine("(Outside of function) Orc has " + myOrc1.health + " health.");

            //////////////////

            Console.WriteLine("======================");

            //////////////////

            int myOrc1Health = 100;
            attackOrc(myOrc1Health, 25);
            Console.WriteLine("(Outside of function) Orc has " + myOrc1Health + " health.");

            //////////////////

            Console.WriteLine("======================");

            //////////////////

            orcEnemy myOrc2 = new orcEnemy();
            attackOrc(myOrc2.health, 25);
            Console.WriteLine("(Outside of function) Orc has " + myOrc2.health + " health.");


            //////////////////

            Console.Read();
        }

        static void attackOrc(orcEnemy enemy, int damage)
        {
            Console.WriteLine("Orc has " + enemy.health + " health.");

            enemy.health -= damage;

            Console.WriteLine("Orc took " + damage + " damage! Orc has " + enemy.health + " health left!");
            
        }

        static void attackOrc(int health, int damage)
        {
            Console.WriteLine("Orc has " + health + " health.");

            health -= damage;

            Console.WriteLine("Orc took " + damage + " damage! Orc has " + health + " health left!");

        }
    }
}

Console Output:

Orc has 100 health.
Orc took 25 damage! Orc has 75 health left!
(Outside of function) Orc has 75 health.
======================
Orc has 100 health.
Orc took 25 damage! Orc has 75 health left!
(Outside of function) Orc has 100 health.
======================
Orc has 100 health.
Orc took 25 damage! Orc has 75 health left!
(Outside of function) Orc has 100 health.

I hope this helps you a bit, and I hope my example is clear considering I don't use C# very often.