status/KillHealStatus.cs
using System;
using System.Collections.Generic;
using System.Linq;
using Sandbox;

[Status(5, 3, 1f, 0, false )]
public class KillHealStatus : Status
{
	public KillHealStatus()
    {
		Title = "Vampire";
		IconPath = "textures/icons/kill_heal.png";
	}

	public override void Init(Player player)
	{
		base.Init(player);
	}

	public override void Refresh()
    {
		Description = GetDescription(Level);

        Player.Modify(this, PlayerStat.HealthRegen, -GetHpDrainAmountForLevel(Level), ModifierType.Add);
    }

	public override string GetDescription(int newLevel)
	{
		return string.Format("Heal for {0} whenever you kill an enemy within 2 meters but lose {1} HP/s", GetPrintAmountForLevel(Level), GetHpDrainPrintAmountForLevel(Level));
	}

	public override string GetUpgradeDescription(int newLevel)
	{
		return newLevel > 1 ? string.Format( "Heal for {0}→{1} whenever you kill an enemy within 2 meters but lose {2}→{3} HP/s", GetPrintAmountForLevel(newLevel - 1), GetPrintAmountForLevel(newLevel), GetHpDrainPrintAmountForLevel(newLevel - 1), GetHpDrainPrintAmountForLevel(newLevel)) : GetDescription(newLevel);
	}

    public override void OnKill(Enemy enemy)
    {
		var distSqr = (enemy.Position2D - Player.Position2D).LengthSquared;
		if ( distSqr > 2f * 2f )
			return;

		var amount = GetAmountForLevel( Level );

		if ( Player.Health < Player.Stats[PlayerStat.MaxHp] )
			Player.TimeSinceChangeHP = 0f;

		Player.RegenHealth( amount );

		//DamageNumbersLegacy.Create( amount, Player.Position2D + new Vector2( 0.2f + Game.Random.Float( -0.1f, 0.1f ), Player.Radius * 3f + Game.Random.Float( -0.2f, 0.3f ) ), color: Color.Green, sizeMultiplier: 0.7f );
	}

	public float GetAmountForLevel(int level)
	{
		return 0.1f + level * 0.5f + (level == 5 ? 0.05f : 0f);
	}

    public string GetPrintAmountForLevel(int level)
    {
        return string.Format("{0:0.00}", GetAmountForLevel(level));
    }

    public float GetHpDrainAmountForLevel(int level)
    {
        return level * 0.4f;
    }

    public string GetHpDrainPrintAmountForLevel(int level)
    {
        return string.Format("{0:0.00}", GetHpDrainAmountForLevel(level));
    }
}