Code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using Timer = System.Timers.Timer;

namespace Typer
{
    public partial class Form1 : Form
    {
        const int INTERVAL = 2000;

        Timer timer = new Timer();
        int index = 0;
        int counter = 0;

        private Font font = new Font("Arial", 30f);
        
        public int Bodovi = 0;
        int indikator = 1;
        
        public Form1()
        {
            InitializeComponent();

            timer.Enabled = true;
            timer.Interval = 40;
            timer.Elapsed += new System.Timers.ElapsedEventHandler(timer_Elapsed);
        }

        void timer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            foreach (Znak znak in Znak.Znakovi)
            {
                znak.Move();
            }

            counter += (int)timer.Interval;

            if (counter >= INTERVAL)
            {
                Znak.Znakovi[index].Alive = true;
                index++;
                counter = 0;
                index = index % 10;
            }

            if (Bodovi > indikator * 100)
            {
                Znak.Speed += 1;
                indikator++;
            }

            Invalidate();
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            foreach (Znak znak in Znak.Znakovi)
            {
                znak.Draw(e.Graphics);
            }

            e.Graphics.DrawString(Bodovi.ToString(), font, Brushes.Green, Point.Empty); 
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            for (int i = 0; i < 10; i++)
            {
                Znak znak = new Znak(this);
            }
        }

        private void Form1_KeyPress(object sender, KeyPressEventArgs e)
        {
            foreach (Znak znak in Znak.Znakovi)
            {
                if (znak.Character == e.KeyChar)
                {
                    znak.Initialize();
                    Bodovi += 10;
                }
            }
        }
    }
}

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;

namespace Typer
{
    class Znak
    {
        
        private static List<Znak> znakovi;
        private Point position;
        private static int speed = 1;
        private Font font = new Font("Arial", 30f);
        private char character;
        private bool alive;
        private static Random random;
        private Form1 forma;

        public static int Speed
        {
            get { return speed; }
            set { speed = value; }
        }

        public static List<Znak> Znakovi
        {
            get
            {
                return znakovi;
            }
        }

        public char Character
        {
            get { return character; }
        }

        public bool Alive
        {
            get { return alive; }
            set { alive = value; }
        }

        public void Move()
        {
            if (alive)
            {
                position.Y += speed;

                if (position.Y > forma.Height)
                {
                    Initialize();
                    forma.Bodovi -= 20;
                }
            }
        }

        public void Initialize()
        {
            character = OdaberiZnak();
            position = new Point(random.Next(0, forma.Width - 40), -50);
        }

      
        private char OdaberiZnak()
        {
            int start = (int)'a';
            int end = (int)'z';

            int poz = random.Next(start, end + 1);

            return (char)poz;
        }
       

        public void Draw(Graphics g)
        {
            g.DrawString(character.ToString(), font, Brushes.White, position);
        }

        static Znak()
        {
            znakovi = new List<Znak>();
            random = new Random();
        }

        public Znak(Form1 form)
        {
            znakovi.Add(this);//dodajemo objekt u listu
            forma = form;
            Initialize();
        }
    }
}