The Halberds & Helmets podcast by Alex Schroeder.
Elephants are cool in war, and they have ivory tusks. Do you want your players to be poachers?
Dwarves are rich and paranoid. There's also a long excursion about dwarves, elves, halflings and humans in the monster manual.
Dragons a dangerous and lucrative and thus provide players with an excellent betting opportunity. Use more dragons!
Doppelgängers are for the urban adventure when you no longer know whom to trust and how to safely uncover the conspiracy.
Crocodiles are ambush predators. I like to announce their presence and treat them like traps.
Creepers are a total party kill in the making with their eight paralysing attacks but I still love them.
Giant crabs are cool because of the crab demon lord Garaskis that offers pincer arms and carapace armour to the poor and powerless.
Chimeras are goofy because of the goat head, but also dangerous for the lion attack and the dragon breath. I use them as guardians of the underworld.
Giant centipedes and other vermin like rats and bats, and monsters like rot grub or green slime are better handled as traps. They don't need to be in the monster manual.
Centaurs are half horse half men, horny drunken violent creatures. Content warning: sexual violence.
A cat for every occasion, from pumas, mountain lions, jaguars, lions to tigers: harassing villages and making it hard to cross rivers
Bugbears are cat people: sneaky, dangerous, serving underground elves, always ready to pounce on you, always spying on you
Boars as pets for orcs, giant boars as mounts for dwarves and halflings, and demon boars as protector spirits of a forest
Talking about giant beetles and how I used them: pack animals for the underworld, war elephants for goblins and the like, or car sized monsters in dungeon corridors
Talking about giant bees, giant wasps, and how I used them: like Aliens in a hive, and as mounts for lizard people
Talking about bears, laser eyes, and summoning angry flying bears
Talking about the basilisk (also known as the cockatrice)
Talking about a simple 2d6 system I use for online gaming. One opposed roll to determine initiative, to hit, and damage.
On the things I do for prep: random tables, monster lairs, jotting down some shallow ideas, run with it in such a way that I don't need to improvise in depth but that shallow encounters point to other shallow encounters, take note of what happens at the table and let that inspire more ideas that build on the previous ones. Last session's shallow idea thus turns into the seed for the next session's good idea.
The gods, the realms, confusing and overlapping portfolios, how even the evil ones need to provide a benefit.
Things to consider when writing RPG text: keeping it short, keeping stats short, keeping it all in one place, don't require leafing around, have art that referees can show to player, have maps that referees can annotate
The mini settings I like to generate where the environment or the map generates inspiration for conflict: the river valleys generate political entities, the swamps and mountain peaks religious entities, add secret societies, a long war somewhere else...
Keep adding where players go, keep track of the open plots, let alpha players push the campaign, involve quiet players, how to plan with your players, negotiate background, and discover personality
Running the wilderness: one hex is one day on foot without roads, using a different random encounter table for every region, how to find their lair, or their tracks
Creating settlements, starting with a few non-player characters, rumours about adventures to be had nearby, the importance of merchants
Running Dungeons, when to roll for random encounters, how much XP to give for monsters, how to restock dungeons
Keep prep short. Use every idea right away. Be impartial and be adversarial. Let them struggle.
No skills. Fewer classes. Quick and random character generation. Smaller bonuses, little damage, few hit points. Rare healing. Simple combat. Treasure is XP. No magic shops. Random encounters.
No clerics. Healing magic makes fights and delves longer. Undead turning makes fights with undeads easier. None of this makes the game better, but instead the Old Testament references break my immersion.
Spells and your repertoire: not being able to copy spells from scrolls and spellbooks and requiring a teacher instead, and not being able to learn more spells than you can cast per day. Also, no research and no crafting.
Movement and reputation, two systems I'd like to use but actually I don't.
Combat: surprise, initiative, d30 rule, not using variable weapon damage, shields shall be splintered, formations, protection, targeting, retreating, fleeing.
Skills: class abilities, the roll to open doors and bend bars, the lucky die of fate, and thieves' skills, they can all be mapped to a 1d6 roll.
Retainers: make sure you agree on how many characters you all bring along. As always, just use pregens. When to make the loyalty check.
Basic terms: player, player character, experience points, level, hit points, saving throw, circle, reaction roll and morale check.
A little something about demon lords: why do their priests survive? They must useful to somebody! I like the ambiguity of the old gods. They are not all good or all evil. And I like the old threefold alignment: Law, Neutrality, and Chaos.
Buildings are a great way to spend money for XP and to let players add to the world. And buildings require servants and guards, and these require wages. And when you take mercenaries along on an adventure, then that also costs money.
Items to fight monsters and oil in particular. How do we use flaming oil? How much can you carry? Encumbrance and the rule of cool. Also: why is plate armour so cheap?
Rolling starting gold and thinking of your parent's background. Social standing? How to buy equipment. The benefits of a character generator, again. The weapons. Fighting from the second rank, again.
Elves are basically fighters and magic users. Halflings and dwarves have better saves and some abilities here and there. Limits on the weapons you can wield. What about armour size? I don't care about level limits since all my games end before we get to level 10.
Thieves and normal humans. How do skill checks work, thieves have better skills, how does surprise work, substituting a d30 for a d20 once a day, max damage, +4 to hit, two handed swords, again; and torch bearers and porters, and magic users wielding weapons, or thieves and magic users wearing armour fight like normal humans
Fighters and magic users. Using descending armour class, to-hit tables, all weapons do 1d6 damage, adding explosions and rays to the saving throws, not having unified advancement tables
Race as class, elves and dwarves in particular. Talking about the gender of elves and dwarves. Talking about the questions Judd proposed for classes, a long time ago.
Talking about the six standard ability scores and wishing I could just rename Intelligence and Wisdom to Education and Yoga. But my players didn't pick it up.
Talking about why we want to write our homebrew games and what old school D&D means to me.