I'd need a little more information to narrow it down exactly but ...
In the early 90's you most likely be playing 4th edition which came out around 1992
The Screaming Skull Catapult was in service from 3rd up to 5th edition
Were you skeleton chariots plastic or metal?
Do you remember what any of the rule books looked like?
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~The ravings of a single mad Goblin is bad enough, but such a power-hungry, malice-filled creature as Mortis can never hope to be understood~