bonus3 bAddMonsterDropItem,n,x,y; Adds a y/100% chance for item n to be dropped, when killing any monster of race x.
0=Formless, 1=Undead, 2=Brute, 3=Plant, 4=Insect,
5=Fish, 6=Demon, 7=Demi-Human, 8=Angel, 9=Dragon,
10=Boss monster, 11=Other than (normal monster) boss monster
If 'y' is negative value, then it's a part of formula
chance = -y*(killed_mob_level/10)+1
http://eathena.ws/forum/topic/379-bonus3-baddmonsterdropitemnxy-doesnt-drop-anything/