I dont know if there is already a thread about this so, I will post it.
It's not so hard to understand and not so hard to do. I was needing to changing it and I started study it.
1st you need is to search the bType and bKind of your item (I mean, item that can ''drop'' another item). I will do it with [Interesting Gift].
So, go on TGAME_GSP > TITEMCHART , and search your item.
Since you found your item, all you need is the bType and the bKind of it.
So, Interesting Gift: bType = 13 ; bKind = 75
Now, go to TGAME_GSP > TGAMBLECHART.
As you can see there are 6 colums:
bType -> the type of using, 13 its when you need to go on the Mystick to unlock it. (Goddess Tear is 13 too)
bKind -> the kind of item you are using (Interesting Gift is 75, Goddess Tear is 0)
wReplaceID -> The item you will unlock (ItemID)
bCountMax -> Everyone knows. Its the max count of the item that you will unlock, so, if you put 5, you can unlock 1,2,3,4 ou 5, that is question of probabilities.
bMinLevel -> Minimum level of the character
bMaxLevel -> Maximum level of the character
wProb -> The probability of the item come out.
So, if I want set the [Interesting Gift] to unlock a potion of fortune. This is what I need to do.
bType = 13
bKind = 75
wReplaceID = (the potion of fortune ID) 18045
bCountMax = (whatever you want) I will put 5.
bMinLevel = 0
bMaxLevel = the max level you want. I will put 93.
wProb = (whatever) I will put 200.
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I repeat, I dont know if there is already a tutorial about this.