I’m fairly sure the numbers are percentage chance for the item to spawn, so your monster has a 40% chance to spawn a single item from the drop list. If an item is spawned the specific item it’ll be is determined semi randomly, with those with a higher number (again, percentage chance) being more likely.
In the following example the Zombie Grenadier will always drop items from two groups, and will always drop a (slightly to severely damaged) chest rig, 0 - 3 manhacks, and has a 50% chance to drop a flashbang hack and another 50% chance to drop a teargas hack, from the “mon_zombie_grenadier” group.
The zombie’s death drops:
"death_drops": {
"subtype": "collection",
"groups": [
[ "mon_zombie_soldier_death_drops", 100 ],
[ "mon_zombie_grenadier", 100 ]
]
},
The “mon_zombie_grenadier” item group:
{
"type" : "item_group",
"subtype": "collection",
"id": "mon_zombie_grenadier",
"entries":
[
{ "item": "chestrig", "damage": [1, 4] },
{ "item": "bot_grenade_hack", "count": [0, 3] },
{ "item": "bot_flashbang_hack", "prob": 50},
{ "item": "bot_gasbomb_hack", "prob": 50}
]
},
I hope this helps!