kill_drop(tab)value
is amount of monsters to kill to engage module in game (I think) to randomize chances to drop item.
In your group this would be like:
after killing 150 mobs with vnum 1093 the server will initiatie a loop to check chances to drop sword+9.
If loop indicates typed number in your group, sword+9 will drop from riper.
If loop indicates different number, you will have to kill another 150 ripers to
engage loop again, and again and again...
I don't know exacly how function for drop items is builded, but I think more less is like I said.
I hope i could help you