One Pawn vs. 44 Pirates: The Strongest Possible Vanilla RimWorld Pawn
To make a 1 vs 40 monster in vanilla Rimworld, you will need all the DLCs except Odyssey. I made a much more detailed guide on Steam guides and Reddit, due to the 5k character limit here.
*TL:DR* You're going to abuse the invisibility psycast, and stack as much psychic sensitivity as possible to maintain it. You're also going to abuse a kill-focused weapon to have infinite psyfocus, while also having the "strong melee damage" gene to one shot enemies.
First thing to do is to breed a suitable pawn. With a good childhood, you get three choices for traits, so pick tough, psychically hypersensitive, and jogger.
Second thing to do is prepare an appropriate weapon. You need the ideology DLC to get a legendary persona Zeus hammer. Set this as your religion's relic as it cannot be obtained in other ways. A zeus hammer is better than a monoblade because high blunt damage is more likely to one-shot a pawn than high sharp damage. You want to save and reload until the relic quest offers the hammer with the "kill focused" trait. Psycasts need psyfocus to cast, so kill-focused allows you to gain infinite psyfocus by killing things (just one-shot weak animals like squirrels if you don't have enough at the start of a battle). If you're trying to get the absolute best in slot, you also want the "psychic hypersensitizer" trait too.
You also need to prepare implants and armors! Get every single implant that doesn't reduce speed or consciousness (e.g. archotech legs, etc.). In terms of armors, you want an eltex shirt, bioferrite slave collar, a prestige cataphract helmet, and some prestige recon armor. You don't get hit very often since you're mostly invisible, so don't get armor that slows the character; focus on things that grant sensitivity and temperature resists.
Next, you need to prepare the psycasts. You absolutely need the invisibility and focus psycasts. Invisibility, at the cost of 45 heat, makes your pawn untargetable for 15 seconds. This effectively makes the pawn immortal, as long as you have a big enough heat meter to maintain it. My pawn has a massive 610 heat meter, and can sustain invisibility for ~262 seconds if she doesn't use other psycasts. The focus psycast greatly improves your pawns speed, and its duration scales with psychic sensitivity. Other psycasts that are valuable to get include stun (allows you to stunlock anomaly bosses like the revenant and nociosphere), berserk/berserk pulse (causes enemies to stay in place and attack each other, otherwise they'll run away from you), waterskip (you encounter a lot of fire traps exploring quest locations), skip (allows you to teleport yourself or enemies), farskip (allows your colonist to instantly return home after transport podding them to a quest location), and word of inspiration (turns excess psyfocus, which you get a lot of, into inspirations for your other pawns).
Next, you need to prepare A LOT of genetics. What you absolutely need are all of archite genes, strong melee damage, and deathrest (enables the use of the glucosoid pump to increase speed, and pyschofluid pump to further increase psychic sensitivity). Just get every non-cosmetic gene in the video. Using this setup, you can pick 4 skills to be good at, and 8 to be bad at; I would suggest being good at melee (duh), medical (lets you rescue enemies for recruitment), social (the psychic reader implant scales your bartering with your high psychic sensitivity), and intelligence (this pawn will later have a x2 bonus to studying anomaly entities, and many quest locations need you to hack something open).
Lastly, you need the anomaly DLC for a few reasons. After beating it, you can make your pawn void-touched. This buff causes the pawn to regenerate fast, become sleepless, study anomalies x2 as fast, and gain 200% physic sensitivity. With void-touched, you're finally ready to 1v20! I would also HIGHLY suggest finding a corrupted obelisk at this point. Upset it, and there'll be a chance to spawn duplicates of your super pawn. Use shock lances to recruit an army of them!!! Other things I recommend from this DLC are juggernaut serums (+melee damage) mind-numb serums (prevent mental breakdowns during psychic drones) and void-sight serums (more sensitivity). This is optional, but you can also mind wipe the pawn to remove inhumanization after getting void-touched. This makes the pawn disturbing, which gives mood debuffs to others, but it lets them to use their massive psychic sensitivity to negotiate with traders/recruit pawns.
There are some more optimizations. You can break a toxic wastepack on this pawns workstation so that the pollution triggers the "pollution stimulus" gene everytime they work, and find a lover to activate psychic bond to further increase sensitivity. Neural superchargers, obtained from the transhumanist ideology, improves your pawn's consciousness, which improves speed. You can get the dark combat preferred precept if you're a darkness colony. Psychophagy ritual too.