After reading Crimson Weapon and Item Random Options maybe you wonder how can I add drop Crimson Weapon like iRO on private server? If you read my topic on rAthena,
Monster Drop with Item Random Option, yet for Item Random Option, you can try implement this Crimson Weapon drop since yesterday for your Ragnarok server.
On iRO -International Ragnarok Online- the crimson weapons are new items. This group of items contain Crimson Spear , Crimson Lance , Crimson Rod  or Crimson One-Handed Staff , Crimson Knuckles , Crimson Violin , Crimson Whip  or Crimson Wire , Crimson Two-Handed Staff , Crimson Revolver , Crimson Huuma Shuriken , Crimson Saber , and Crimson Bow . Yet some people on iRO calls the Crimson Weapons as Scarlet Weapons.
How does Crimson Weapon drop?
Some crimson weapons were added to monster’s drop list by replacing old drop from some monsters. Example for Pasana, it drops Crimson Dagger  and Crimson Saber  replacing Falchion  and Stiletto . See the ‘old’ Pasana Drop here, and this for new Pasana drop list that drop Crimson Dagger  and Crimson Saber .
For the full list of monsters that drop Crimson Weapons, please look at news on iRO official website Episode 15.2 Crimson Weapon System.
What is relation between Crimson Weapon and Item Random Option?
Crimson Weapons on iRO are endowed with random element when the item is dropped by monster. iRO calls it as charmed. Player can obtain Crimson Weapon with different element for same weapon from same monster.
Example for Pasana, player kills Pasana then gets Crimson Saber  (aka Crimson Sabre ) has chance it will charmed with Water element. In same time, other player kills Pasana then gets Crimson Sabre  with Fire element.
But, Crimson Bow  and Crimson Revolver  will never be charmed!
How to add drop like Crimson Weapon on Ragnarok server?
- It’s recommended to use latest rAthena or at least since Item Random Option system was implemented.
- Download this diff file for Monster Drop with Item Random Option: mobdrop_randomopt.diff.
- You can apply or patch that diff file or maybe add it manually.
- Add the Crimson Weapons in random option group by editing item_randomopt_group.txt, in this file you can add more random group for dropped item.
- Add the Crimson Weapons as monster drop in your Ragnarok server by editing this mob_drop.txt file.
- Now your Ragnarok server is ready for Crimson Weapons!
Here are screenshots I took while test this Random Option Drop on my offline Ragnarok server, not for Crimson Weapons. But for custom drop for Valkyrie Randgris that added Valkyrian Armor and Valkyrian Shoes  as additional drop and MVP Reward.