I'm trying to work out the last of these today.
As it stands now monsters are incredibly similar to characters except for item drops/steals, equipment, skill/spell management, etc. They probably need a few more variables for basic AI like spell-happiness rate, counter-attack, whatever.
There are 32 flags for enemy "families", the same with classes - so an item can do extra damage to a Giant family, and likewise enemies can have class bits set.
IA for 1.0 has to go inside a script "<monster-name>" otherwise the base script "Monster" is run with default AI if it is not overridden.
Monsters will have lists of abilities, but not like the NES version (which has lame AI), so they can be a little smarter in their special attacks. (Should each ability in the list have an adjustable rate, or each category of ability?)

Consequently items have a very similar structure to these as well, due to them being equippable. I think spells are the only thing that are very different.