"Pawns"
often used to refer exclusively to a player's colonists. For example, the recommendation that "You only feed cooked meals to your pawns" would likely only be referring to colonists, and would not be inclusive of tamed animals that would also fit under the technical definition of "your pawns". - official Rimworld wiki
Mental breaks
A mental break is a pawn event that may occur when a pawns's mood drops below the mental break threshold. Majority types of mental break cause a mental state, during which the pawn will become uncontrollable and shirk work tasks for a short while, or even worse, they will attempt to sabotage the colony. A breaking colonist may be interrupted by arresting or downing them. A few types of mental break, like catatonic breakdown or crisis of belief, do not cause mental state.
There are three levels of severity for mental break events: minor, major, and extreme. Each severity level has a different pool of possible events that may occur at different frequencies. Minor events include hiding in the pawn's room for a day, extreme events include murder.
Colonists, visitors, enemies, tamed, and wild animals all have types of mental breaks. - official Rimworld wiki
Psycasts
An organic connection to a larger psychic field. This allows a person to psychically induce a distant archotech superintelligence to influence reality in ways that seem impossible. Higher levels of psylink permit the use of more powers. Regardless of psylink level, a person can only use specific powers that they have learned. Psylink comes from a variety of sources. Single-use psylink neuroformer devices can create a psylink. Tribal peoples also know how to develop it through ritual linking with the legendary anima tree. As a physical phenomenon in the brain, psylink is poorly-understood by scientists, not least because it seems to actively conceal itself if studied too closely. One thing most agree on is that it somehow connects people to archotechs and harnesses their power, possibly through some sort of negotiation or sympathy mechanism.
Storytellers
The AI storyteller is the main mechanism used to determine game difficulty and play style. There are currently three presets for narrative settings. Each preset features different raid frequencies and an eponymous cartoon mascot. The player must choose either Cassandra Classic, Phoebe Chillax, or Randy Random to act as their "unseeable God." They will periodically create events for your colony, including pirate raids, resource drops, or manhunter animal packs. The AI Storyteller does not have an in-game body, location, or manifestation; it is just a name given to describe game settings.
Your choice of storyteller sets the tone for your colony - a more benevolent storyteller like Phoebe will send trade caravans or helpful travelers after hitting your colony hard with a tough raid.
The frequency and type of storyteller events are based on a number of factors. Colony wealth, building wealth, colonists count, animal count, if a colonist has died or been severely wounded recently, and how long it has been since the last major event are all considered before a storyteller event occurs.
The difficulty is adjusted separately from the storyteller, however, some storytellers are less merciful than others. - official Rimworld wiki
Cassandra creates story events on a classic increasing curve of challenge and tension.
She'll push you with dangerous events, then give breathing room, then come back to push once more.
Phoebe gives lots of time between disasters to build your colony.
But beware - at high difficulties, she'll hit as hard as anyone.
Randy doesn't follow rules.
He'll generate random events, and he doesn't care if they make a story of triumph or utter hopelessness. It's all drama to him.
Warning: Since Randy is truly random, he will sometimes send extremely difficult or unfair groups of events at you.
It makes for high drama - and unavoidable sacrifices.
