The Function of "Tricks"

The "trick" or "special" encounter is an important element of D&D. But though trick encounters are mandated in the "chamber contents" table, they have gotten short shrift in the official rules. I have often floundered attempting to implement them in adventures. (Especially in my B/X experiments, in which 1 in 6 encounters are "Special.")
In this post, I am trying to clarify my approach to them, and to create a process which can be easily and harmoniously implemented in adventure design.

This post is largely inspired by This entry in Tao of D&D. In which Alexis proposes that Monsters can be categorized by their relationship to the environment, and by extension, how they function in encounters.
Alexis puts forth 5 broad categories to define what kind of encounters a monster can provide, based on their ecological niche. In subsequent posts, Alexis shows how this provides a rationale which frees the DM from the arbitrary caprice of a random encounter table, and demonstrates how this Monster-Rational can be used to design an adventure to damn-near-completion in relatively little time.
This line of thought is frankly the most useful DMing advice I have ever encountered in the blogosphere. It is simple and effective, and a little painfully obvious after it has been spelled out for you.

The essence of this advice, I think, is that a DM should not be distracted by the Form an encounter takes, but should make design choices based upon the Function of the encounter. So rather than arbitrarily inserting a random trick in room x, the DM will select tricks based upon what makes sense in context and what serves the flow of the adventure.

After a little brainstorming, here are my Functional Categories for Tricks:

Art and Installation Pieces: Meant to inform or entertain explorers, or waste their time. A corpse trapped in amber, a distinctive sculpture of an unknown creature. A friend of mine ran a dungeon where we found a painting of an NPC we had met before, with someone else we had not. Little did we know that the scene in the painting hinted at a deeper conspiracy.

Debuff: Meant to disable, or confound a character's usual capabilities. This includes anything which damages a character's numbers, and more subtle effects which confuse or interfere with them. For instance, evil plants which are basically harmless, but would still confuse an attempt to  detect evil.

Environment Changer: Changes the layout or environmental effects of a location, perhaps opening or closing paths or creating new challenges. A switch which opens a floodgate and drains a pool, revealing a previously submerged passageway would be an example of this.

Environmental Effect: Incidental to the environment, but with a tangible effect upon the PCs: Smoke, extreme heat or cold, gravity shifts, magical fields. Possibly subject to and Environment Changer.

Evidence of Influence: A mysterious effect which hints at the presence of a significant creature or NPC, perhaps intelligent or powerful. In a friend's campaign, we came upon a valley populated by basilisks and archerai. But oddly, they did not attack us. Suddenly, a mighty Roc appeared and snatched up one of these hapless monsters while we hid in a nearby ravine. We were later to learn that this odd ecology was the work of a powerful NPC we were soon to meet. But the sheer mystery of the moment and the sudden tension makes this scene my favorite moment from that campaign. Or it could be something less spectacular, like an alarm spell or arcane eye which give evidence of a nearby wizard.

Lure: Bait to tempt the PCs into danger. The danger may be hidden or obvious.

Qualifiers: An encounter which is meant to limit, but not entirely bar access to something. If an ancient wizard wanted to preserve his library for posterity, while ensuring that it would be properly appreciated and used, these are the kinds of encounters you might place in his tomb/laboratory

Scarecrow: A threat which seems credible from the PC's perspective and dissuades them from a certain course of action. Might be placed on purpose by an intelligent creature, or incidental to the environment: A giant, complete skeleton sits athwart a passageway. Think it will animate and attack,  or did it just lay down and die there?

Secret Doors, Hidden Objects: Any case in which access to something is obfuscated, whether by design or merely incidentally. 

Tool: An object or effect which serves a useful purpose, even if that purpose is unknown or surprising to the players. This should be relevant to the setting: A Zone of Truth cast in a magistrates' chambers, or a statue which translates languages in a public plaza, or an apparatus which extends a bridge over a chasm.

Transporters: A trick which moves characters or objects, either for good or ill, by mundane or magical means. Collapsing floors, rotating walls, powerful torrents of wind or water,  and being picked up and carried to Anor Londo by demons are examples of this. 

Not included in this list: The Time-Waster

Of course these categories are broad, and not the specific forms of Tricks. I figure that when you want to include a trick, the broader context should inform the specifics.

For help with specifics of Form, I suggest "Tricks, Empty Rooms & Basic Trap Design" By Courtney C. Campbell. It is a very interesting and useful document for adventure design. I would describe it as the equivalent of the Monster Manual for Tricks and Empty rooms. It provides a great list of examples and Forms of tricks. But like the MM, it neglects Function and context.

This Function First design is predicated on the idea that a D&D scenario should make sense. If there is an underlying rationale for the encounters, then I think that structure makes the game more fair. If the players can discover that rational, it offers another point of engagement to the game, and provides a tool for Agency.
The opposite of Function First design would be Form First design. This is equivalent to building and running adventures from random tables. I have spent plenty of time trying to build adventures in this way, trying to discover and reproduce the "implied setting" of the tables in the official books.
But the content produced in this way has almost always fallen flat. It fails to produce tension, and generates things which just don't make sense.
The dice-roll says wild dogs appear, and that they are friendly. I convey this to the player, and I can feel the game implode.
Using the Form-first, random generation approach to Tricks and Special encounters gives us stuff like a Book which Reduces/Enlarges a character, or a Pool which Grants a Wish. These two examples are fairly coherent as these things go. But now the burden is on me as a DM to actually run these encounters and make them interesting and relevant. Then suddenly, my adventure-building flow is staunched and I need a drink.
So in order to protect my liver, I am embracing Function-First design.

This work on Trick categories is tentative, and subject to later refinement. If you see any glaring omissions, or if you have good or bad results with this idea, let me know in the comments.