Here is a boss who has a certain number of lives and a certain retaliatory damage. You have 4 spells to deal damage to the boss. The program ends only after the death of the boss or the death of the user.

Boss fight

namespace MyCode
{
    internal class Program
    {
        static void Main(string[] args)
        {
            const string CommandDefenseAura = "1";
            const string CommandLayOnHands = "2";
            const string CommandMagicPower = "3";
            const string CommandUseWarhammer = "4";
            const string CommandUseSmite = "5";

            Random random = new Random();
            int lowHealthPoints = 0;
            int bossMaxHealthPoints = 250;
            int bossMinHealthPoints = 100;
            int bossHealthPoints = random.Next(bossMinHealthPoints, bossMaxHealthPoints);
            int bossDamage;
            int bossMaxDamage = 20;
            int heroMinHealthPoints = 10;
            int heroMaxHealthPoints = 80;
            int heroHealthPoints = random.Next(heroMinHealthPoints, heroMaxHealthPoints);
            int heroWarhammerMaxDamage = 10;
            int heroWarhammerDamage;
            int heroHeal = 15;
            int heroSmiteDamage = 10;
            int magicExtraDamage = 10;
            int heroDefenseAura = 0;
            int heroSmiteCounter = 5;
            bool heroMagicWeaponIsActive = false;
            bool defenseAuraIsActive = false;
            bool enteredTextIsUnknown = false;
            string enteredCommand;
            string menu = $"{CommandDefenseAura} - to use Defense Aura, Aura gives you a bubble defense for 3 rounds (you don not get damage for 3 rounds)\n" +
                    $"{CommandLayOnHands} - to use healing spell and restore {heroHeal} HP\n" +
                    $"{CommandMagicPower} - to add Magic Power ({magicExtraDamage} Damage) to your Warhammer\n" +
                    $"{CommandUseWarhammer} - to attack using Warhammer (up to {heroWarhammerMaxDamage} Damage)\n" +
                    $"{CommandUseSmite} - to use Smite Damage ({heroSmiteDamage} Damage), but only {heroSmiteCounter} times\n" +
                    $"Type any Key to show menu again.\n";

            Console.WriteLine($"You are in a final room of the dungeon!\n" +
                $"You are The Mighty Paladin and you have to kill the dungeon boss!\n" +
                $"For that you can use next spells:\n" + menu);

            while (heroHealthPoints >= lowHealthPoints && bossHealthPoints >= lowHealthPoints)
            {
                heroWarhammerDamage = random.Next(heroWarhammerMaxDamage);
                bossDamage = random.Next(bossMaxDamage);

                Console.WriteLine($"You have {heroHealthPoints} HP, Boss have {bossHealthPoints} HP");
                Console.WriteLine("Enter your command!");

                enteredCommand = Console.ReadLine();

                switch (enteredCommand)
                {
                    case CommandDefenseAura:
                        int maxDefensLength = 3;
                        
                        defenseAuraIsActive = true;
                        heroDefenseAura = maxDefensLength;
                        break;

                    case CommandLayOnHands:
                        if (heroDefenseAura > 0)
                        {
                            heroHealthPoints += heroHeal;
                            heroDefenseAura--;
                        }
                        else
                        {
                            Console.WriteLine("You cant use Lay On Hands spell without Defense Aura on you!\n");
                        }

                        break;

                    case CommandMagicPower:
                        Console.WriteLine("You are praying to God to enhance your weapon power for the next time you use Warhammer (this round you can't attack!)\n");
                        heroMagicWeaponIsActive = true;
                        break;

                    case CommandUseWarhammer:
                        if (heroMagicWeaponIsActive)
                        {
                            bossHealthPoints -= heroWarhammerDamage + magicExtraDamage;
                            heroMagicWeaponIsActive = false;
                            Console.WriteLine($"Boss get {heroSmiteDamage} + {magicExtraDamage} damage");
                        }
                        else
                        {
                            bossHealthPoints -= heroWarhammerDamage;
                            Console.WriteLine($"Boss get {heroWarhammerDamage} damage");
                        }

                        break;

                    case CommandUseSmite:
                        if (heroSmiteCounter > 0)
                        {
                            bossHealthPoints -= heroSmiteDamage;
                            heroSmiteCounter--;
                            Console.WriteLine($"Boss get {heroSmiteDamage} damage");
                            Console.WriteLine($"You have left {heroSmiteCounter} Smites!\n");
                        }
                        else
                        {
                            Console.WriteLine("Smite is unavailable!\n");
                        }

                        break;

                    default:
                        Console.WriteLine(menu);
                        enteredTextIsUnknown = true;
                        break;
                }

                if (enteredTextIsUnknown == true)
                {
                    if (defenseAuraIsActive)
                    {
                        Console.WriteLine($"Defense Aura is Active! You have {heroDefenseAura} rounds of Defense Aura left\n");
                    }
                    else
                    {
                        heroHealthPoints -= bossDamage;
                        Console.WriteLine($"Hero get {bossDamage} damage");
                    }

                    if (heroHealthPoints > heroMaxHealthPoints)
                    {
                        heroHealthPoints = heroMaxHealthPoints;
                        heroDefenseAura = 0;

                        Console.WriteLine("Your HP is on Max, Defense is deactivated!");
                    }

                    if (heroDefenseAura == 0)
                    {
                        defenseAuraIsActive = false;
                    }
                }
                else
                {
                    enteredTextIsUnknown = false;
                }  
            }

            if (heroHealthPoints <= lowHealthPoints && bossHealthPoints <= lowHealthPoints)
            {
                Console.WriteLine("WOW! It is a draw!");
            }
            else if (heroHealthPoints <= lowHealthPoints)
            {
                Console.WriteLine("Hero is dead! You lose!");
            }
            else if (bossHealthPoints <= lowHealthPoints)
            {
                Console.WriteLine("Boss is dead! You win!");
            }
        }
    }
}