A pitch deck in OSR+ is a visual presentation of your premise. It helps illustrate the sort of game you want to play.
Below you will find a pitch deck for God Beyond the Portal, a (forthcoming) world of OSR+ that's about a mysterious eclipse which has brought the heroes together in a supernatural conspiracy involving a religious cult. In God Beyond the Portal, there are stress mechanics that simulate heroes' descent into madness. It's HBO-prestige television like The Leftovers set in a Ravenloft-like setting with supernatural horror inspired by At the Mountains of Madness by HP Lovecraft.
Illustrate the Premise
The pitch deck teases out the premise in a series of images that evoke the mood and setting. You can use images from your favorite films, games, or graphic novels, or try your hand at AI to generate exactly the images in your mind. All that matters is that you have something interesting for players to look at while you go through your presentation.
Kick off session zero with some drama and immersion. Play some music that is evocative of the mood you're going for, and slowly read aloud what you've written to expand upon the premise. Keep it short, but impactful. Let things sink in, and don't be afraid of the silence as your players contemplate your premise.
Ask Evocative Questions
At this point, your players are probably thinking about how their characters might fit into the world. Ask them a pointed question that their characters will need to answer in session zero, that is central to the premise. They don't need to answer now, but it's a question that will sit with them as they enter session zero. In God Beyond the Portal, the premise demands that the heroes have been brought together in the rebel province Idania as a result of an eclipse called the Long Night, so we ask: "Why did you flee to the edge of the world?" and "What did you lose to the Long Night?"
Factions help players conceptualize their characters by juxtaposing them with something concrete in the premise that’s already operating in the fiction. Factions are part of your agenda as a GM and should feature prominently in future sessions as you flesh out the adventure. Each world of OSR+ will provide a number of factions to choose from, but if you're coming up with your own factions, you should have at least one or two more than the total number of players at your table. (So if you have four players, present five to six factions).
Paint Factions with a Broad Brush
You don't need to know much about your factions when you present them: only what they want with respect to the premise, and how you envision them from an aesthetic point of view. You want to keep things vague because the conversations you'll have with your players in session zero will help you solidify the details with the story hooks they develop. You never know how important a PC will be to a faction (in fact, they may end up in charge of it!), so you don't want to come into session zero having too strong of a preconception.
In God Beyond the Portal, we present the following factions:
The Mora Seers
This faction is represented by peoples native to the city where the PCs start the adventure, who are persecuted by an invading Empire. We evoke the itinerant gypsy as a trope, painting the picture of an ancient culture whose elders possess mysterious powers in connection with the central mystery.
Archers of the Watch
This faction is made up of terroristic street rebels who openly oppose the invading Empire. We evoke Robin Hood-like woodsmen trope that operates in the shadows outside the city limits.
Here we have opportunistic outsiders who are trying to capitalize on the chaos of the occupation in the city. The Retainers evoke the colonizing treasure hunter trope, driven as they are by a profit motive.
The Prince Regent
These are Imperial traitors who secretly oppose the Emperor and his occupation. The trope of the rebel prince as the underdog serves as a middle group between the outright terrorism of the Archers and the parasitism of the Retainers.
The ILLUMN LAITY
Finally, this faction represents the religious cult at the heart of the premise. Are they foes or allies? We might already have an agenda for them, but by presenting them neutrally to the players, we open ourselves to story hooks created by the players that may change our preconceptions about them.
At the conclusion of session zero, we ask the players to affiliate their PCs with one of these factions. This anchors their PCs more explicitly to your agenda.
Remember that in lieu of factions, any concrete context from the fiction will do. For example, in A Quest of Queens, players affiliate with one of the gods from that setting's pantheon of gods.