Add a monster book: Common this feature is used in many games and some players would like to know some monster description and this books or pages can be also used as a form of market i think many players will like this idea.
On this idea add the ability to get some monster stat based on the monster himself could a nice add for players and make a search for diferent ways of damge.
Monster cards FTW!
((redacted, the name might mention runes and magic)) has this. Monsters will drop on a relatively rare basis a "monster card" showing the same type of monster that dropped the card e.g. a Desert Scorpion as found in the Dead Sea area would drop a Desert Scorpion card, and bosses, of course drop their own boss card. Every character has a collector's book where the character can stash one copy of a particular card, gaining stat points. Surplus cards are tradable to merchants and/or other players (often for substantial amounts of money). My recollection (it's been a couple of years now since I last played) is that mobs drop these cards on a frequency similar to silver anniversary coins, maybe not quite as rare as that, and the drop rate seemed to depend on the monster as well. Some cards were reasonably common in the auction house because people fought the monsters a lot, other mobs almost never got attacked, so you *never* saw the card. (I'm thinking here of a particular dog-like monster of around level 50 that (a) had a fairly wide aggro bubble, and (b) put a bleed on you that was dangerous even for level 60+ characters, so people tended to leave them alone after having done an end-run around them. I cheated slightly and used my rogue's stealth mode to sneak past and unlock the teleport destination beyond.)