PoMNPC.cs

using Terraria;
using Terraria.GameContent.ItemDropRules;
using Terraria.ID;
using Terraria.ModLoader;
using static Terraria.ModLoader.ModContent;

namespace PathOfModifiers
{
    public class PoMNPC : GlobalNPC
    {
        public override void ModifyGlobalLoot(GlobalLoot globalLoot)
        {
            var isHardmode = new LeadingConditionRule(new Conditions.IsHardmode());
            isHardmode.OnSuccess(
                new CommonDrop(
                    ItemType<Items.ModifierFragment>(),
                    1,
                    PoMGlobals.DropRate.Fragment.fromBossHardmode,
                    PoMGlobals.DropRate.Fragment.fromBossHardmode));
            isHardmode.OnFailedConditions(
                new CommonDrop(
                    ItemType<Items.ModifierFragment>(),
                    1,
                    PoMGlobals.DropRate.Fragment.fromBoss,
                    PoMGlobals.DropRate.Fragment.fromBoss));

            var isPostPlantera = new LeadingConditionRule(new Conditions.DownedPlantera());
            isPostPlantera.OnSuccess(
                new CommonDrop(
                    ItemType<Items.ModifierFragment>(),
                    1,
                    PoMGlobals.DropRate.Fragment.fromBossPostPlantera,
                    PoMGlobals.DropRate.Fragment.fromBossPostPlantera));
            isPostPlantera.OnFailedConditions(isHardmode);

            var isBoss = new LeadingConditionRule(new Conditions.LegacyHack_IsABoss());
            isBoss.OnSuccess(isPostPlantera);
            isBoss.OnFailedConditions(
                new PoMGlobals.DropRate.CommonDropScalingWithValue(
                    ItemType<Items.ModifierFragment>(),
                    PoMGlobals.DropRate.Fragment.chanceDenominator,
                    PoMGlobals.DropRate.Fragment.baseMin,
                    PoMGlobals.DropRate.Fragment.baseMax,
                    PoMGlobals.DropRate.Fragment.multiplyPerValue));

            globalLoot.Add(isBoss);
        }

        public override void ModifyActiveShop(NPC npc, string shopName, Item[] items)
        {
            if (npc.type == NPCID.Wizard)
            {
                foreach (Item item in items)
                {
                    // Skip 'air' items and null items.
                    if (item == null || item.type == ItemID.None)
                    {
                        item.SetDefaults(ItemType<Items.ModifierFragment>());
                    }
                }
            }
        }
    }
}