In Defense of Normal
Y'all are being too weird with it, cut it out. No seriously, all those custom classes, monsters, items. Why?
Creation is sick and awesome. I wouldn't be here if I didn't like writing new tabletop things and sharing them with people, or playing in strange settings and strange worlds. Roleplaying and the creative aspect that goes alongside it is awesome. That being said, there's a HUGE tradeoff between the novelty of new ideas and the ease with which they come up at the table that I don't see people talk about basically ever. I'll try and illustrate what I mean with an example based on experiences that I've had at the table.
The Normal Example:
Bob wants to put a strong enemy in his dungeon. He uses his monster generator of choice, one that he stole from some retroclone or another, and rolls a vampire. He puts the vampire in, names it Dracula, and proceeds to the next room.
During play, he describes the vampire's pallid skin, sunken eyes, and blood-soaked chin. Cassie, a veteran of speculative fiction, leaps from her seat and shouts "A vampire!" Everyone at the table knows what a vampire is, so they start to strategize. "Do you have any holy water?" "How about wooden spikes?" "We need to be careful of its Gaseous form!" Play continues on apace, the vampire is slain or otherwise dealt with. Everyone cheers. They've just slain Dracula!
The Weird Example:
Bob wants to put a strong enemy in his dungeon. He uses his monster generator of choice, one that he stole from some retroclone or another, and rolls a vampire. Vampires represent a serious ontological threat to his finely-crafted world. He spends a long time thinking about what "Vampire" means in the context of his setting. He comes up with bespoke powers, descriptions, and an appearance for this ostsensibly new creature. He is proud of his work and excited to show it to his players. He names it Crokenoffen and proceeds to the next room.
During play, he describes the vampire's oily complexion, it's saucer-like eyes, and long jelly arms. Cassie, a veteran of speculative fiction, strokes her beard. She is nonplussed. She uses the resources of the game at her disposal. She engages with the knowledge mechanics, interrogates the environment, and experiments with what little time she has to interact with the creature. While other players die hopelessly at the hands of the best, they uncover the powers and abilities that the creature has and Cassie makes careful note of them from the back rank (Cassie always plays a wizard, the safest class). In the future, encounters with this type of creature will be easier!
There are two things I want to point out here. The first is that in the first example it is much easier for other players in the game to contribute meaningfully to the encounter. Everyone knows what vampires are, how they work, and what they typically want. This shorthand allows a table to skip the "investigation" stage entirely, moving straight into the action phase where play happens (and all the fun stuff that that entails). In the second example, the unknown begets further questioning and invariably slows down the game. Good gamers ask questions, interrogate the fiction, and try to scrape together an understanding of the thing in question. Much more game time is spent in the "comprehension" stage of the game, where players and the referee are trying to come to a shared understanding of what is happening. After they comprehend the reality of the situation, they spend more time in the "investigation" stage, whereby they try to poke and prod at the novelty to discover its features. Only once they've discovered enough to deal with the creature do they move to the "action" phase (these phases are not discrete but fluid parts of any conversation, even outside of RPGs, and aren't really the focus of this post).
Interacting with anything novel, whether it is rules, monsters, items, places, or people, will slow the game down. This isn't a bad thing by any means, but it is an often-understated aspect of adding in novel shit to your game. If overused, it can make the game feel slow, ponderous, and inconsequential.
What is Normal?
How do we avoid this? The answer is simple. Use more Normal shit. Normal shit can be anything, really, but the key concept is that your players understand it already. Vampires are a good example because they're reasonably complex in D&D and most people who play these sorts of games know how they work (and even those that don't have some incomplete idea). There will be less time spent investigating the features of something and more time playing out interacting with it.
The important thing about Normal is that it's normal relative to whoever you're playing with. I am, unfortunately, intimately familiar with a lot of tropes from classic D&D modules. Bree Five-ee may not be familiar with the glorious white ape. What is Normal to one table is Novel to another.
Too Much Normal
Normal is not without its haters. Many of you are haters of the norm. You gnash your teeth and stomp your feet at the Orc and the Kobold and the Goblin. I have joined your ranks on occasion. Too much Normal in a game can make it feel stale, uninspired, and cliche. Players fantasize about new magic systems. The referee stays up late at night thinking about other games or that module they read last week. The experience suffers.
It goes without saying that Too Much Normal varies wildly, from table to table and from play culture to play culture. In some circles, homebrew is frowned upon. In others, if you ain't homebrew'd, you're naught but a toad, dude. Learning where the line is for the style of game you're running and who you're running for is unfortunately only developed through time playing.
Arcade games, for example, benefit greatly from lots of Normal. Arcade Gamers don't really care about the investigation of the unknown, preferring instead the thrill of d20 gambling. Life is a highway and for them, their foot is pressed too close to the metal to notice the roadkill on the side of the road. The Weird actively harms the experience of Arcade Gaming in many cases.
In contrast, Horror games and their gritty-OSR cousins are basically meditations on the Normal punctuated by brief incursions from the Weird. Vast swathes of Normal punctuated by brief moments or encounters with the Not Normal heighten the wonder (or terror) of discovery. The mundane (in the context of an adventure game) can't be horrifying, but without it the truly horrible means nothing.
Further still, some games eschew Normal entirely. Hop between planes with the best of them, riding dolphins with lazer eyes one moment and swimming with Conan the Barbarian in a golden lake the next. The joy is in the Not Normal, relishing in the unexpected and the novel.
Even within a setting, absent any playstyle of game, you can partition Normal and Weird differently. Many games or styles of games have a "Normal World" Where things function about like everyone at the table would expect and then a "Weird World" full of things that break from that expectation. To clarify here, I'm not talking about the mundane vs. magical (though this is often where the Normal/Weird distinction lies in a worldbuilding level) but the discrete parts of the world players can understand at a glance vs. the things that they can't.
The Takeaway
My remarks above all boil down to a cry to be more intentional with how you divert from the Normal at your table. Understanding what leaving Normal does for your game can help you understand how to better facilitate the game with the Weird things you want. Don't just reach for the weirdest, most out-there concept you can find on first principle. Take a measured, intentional approach to the Weird things you put in your game and how your audience (the players) will handle it. Most of the time, using something Normal will be better than using something Weird.