If ur after particular drops (like maybe spider-based drops from spiders) you could do something more specific, like:
EVENT: Unit Dies
CONDITIONS:
OR Any Conditions are true
[Unit type of (Dying Unit) equal to (Spider 1)]
[Unit type of (Dying Unit) equal to (Spider 2)]
EVENTS:
Set Variable (Spider Drops) = Random Integer between 1-10
IF ((Spider Drop) equal to 1) THEN (Create (Spider Part) at position of (Dying Unit)) ELSE (Do Nothing)
IF ((Spider Drop) equal to 2) THEN (Create (Spider Part 2) at position of (Dying Unit)) ELSE (Do Nothing)
IF ((Spider Drop) greater than 2) THEN (Do Nothing) ELSE (Do Nothing)
Ok, I got a lil carried away, but its a useful way of doing it for RPGs and the like.