Personality inventory? Like, "What are the important elements of my character's personality, and do I want it to stay that way?"
On the face of it, this kind of sounds like something you'd expect to see in a very modern game. In fact, this is a very subtle process, and until recently, I hadn't really been consciously aware of it. A year or so ago, I could've talked about the hell I put clerics through in my campaigns, which is an extreme example of what I'm talking about here. If it's more comfortable for you, think about this as stress-testing the character concept. The goal here is to make the character change with time in subtle and interesting ways.
intriguingly dark and doomed characters. For certain sort of player, this is the stuff excellent gaming.
All well and good, but the point isn't to create an angst-fest where you just constantly dump horror and tragedy on the characters’ heads. Instead, the goal is to make the non-mechanical, more subtle aspects of characters important in the game. They're all sorts of little ways you can do this; old school games are rife with this sort of thing. Changes to the character, or the character’s circumstances, necessitate reevaluating the place of that character in the setting in relation to nearby cultures and how the character is expressed through play, the setting of goals, and the various attributes of personality. And you can find the mechanisms for this all over the place in the games you already play.
Charm: the granddaddy of them all. Even the otherwise laconic Moldvay rules mention “orders against [the target’s] nature (alignment and habits) may be resisted". These sorts of spells really get to the heart of what a character wants and what they're willing to do to get it. It's very much an invitation to review how the character has behaved up until this point. Characters willing to stab their comrades in the back to get what they want are less likely to resist these sorts of spells than those who adhere to a very strict code of honor. Most characters fall somewhere in between these two extremes, of course, but the basic principle remains. Who they've been and what they've done dictates how the spell works and its limitations.
Transformations: changes in circumstance require changes in behavior. Let's start with the most dramatic: polymorph other. A character who's been transformed into another race or even class is going to find people treating them differently. Their role in the party he changed. More importantly, their role in society may have changed. The extreme example is, of course, xenophobia. The elf becomes an orc, or the champion of the dwarves becomes a goblinoid. However, there are much more subtle options. A human transformed into a gnome suddenly has to deal with a world built for people twice his height. An elf turned human suddenly has their life expectancy drop to 10% of what it was before. Moving to or from the dominant form of life in a particular area can have significant consequences for characters’ social standing and opportunities. And we haven't even touched all the fun you can have shifting genders.
Things can get even more fun if you cast your net a little more broadly for opportunities. Usually, a character infected with lycanthropy or turned into an undead is no longer playable. However, you can have a lot of fun with the character who is trying to live with such a condition. Disfigurement in combat can subtly alter how a character interacts with the world, or even force them to be more dependent on others. Gaining the ability to use spells at higher levels can also dramatically transform how a character is perceived and in turn how they behave.
Such displays almost invariably change the opinion of those who witness it. It would be odd indeed if characters who had saved the realm a handful of times, defeated menacing ogres, and slew giants and dragons were not treated differently by those whom they had both helped and thwarted.
How players and their characters deal with success can be as telling, and is interesting, as how they deal with adversity. Into every life a little sun must shine, and most people don't pay as much attention to how they handle success. Good times are seen as a chance to let your guard down. The true nature of the character may be revealed in such moments, often with consequences that outlive any momentary good fortune.
Again, this is not something overt and certainly not something that should interfere with gametime. Instead it is very much part of the give and take of play. Characters change, and the world reacts to that change. Characters then react to the world’s reactions. This creates a chain of events that follow logically from each other in ways that are largely predictable, but allow for great variations. This is where players craft their characters. This is where two fifth-level fighters exhibit their unique individuality from each other. This is where the magic happens. This sort of thing is far more flexible, and infinitely more powerful, as well as frankly more interesting, than anything mere mechanics can achieve.
Art by Joseph Mallord William Turner and Claude Vignon.