There are three kinds of options that, so long as they are well organized that really never become clutter and no matter how many you have any game came benefit from them
1st, Magic Items
You can never have too many of these for a campaign, not only to add variety but also to make jaded players happy. Instead of yet another +2 sword, nothing lights up a players eyes faster than something cool like a Sword of Thorn-Spray or something cool.
Since you get to control which of these come into the game, I figure you can never have too many well thought out balanced interesting spells. Now most of the time you'll only use one or two of them in any given encounter, but in a long campaign, well, more spells is not going to be too much of a good thing. Why I especially enjoy having a variety is that it keeps those jaded players who think they have seen everything on their toes and gets them more involved .
And yes I have been players side of this, I love it.
I rarely use monsters but so long as they are well divided by type, you can never have too many. Even enormous books like the upcoming Compiled Tome of Horrors (1000 pages!) are not wretched excess. Instead its simply more variety and thats a fine thing .
Needless to say the Magic Item Compendium and the Encyclopedia Magica (back from 2e) along with the various random magic item systems , the Spell Compendium and 2e's Wizard and Priest Compendiums were among my favorite books. So much good stuff for the plucking ...
Mythic Babylon cover - My friend and gaming colleague Chris Gilmore (‘Hartmut Hare-Eye’) is the co-author of the forthcoming *Mythras* setting book *Mythic Babylon* (it will be p...
3 days ago