Digimon World 1 Walkthrough (Chapter 2)
This Chapter will cover the end game portion of Digimon World. It's hard to say exactly when the end game begins, but I would consider Factorial Town to be the real start. Most of the Digimon found in Factorial Town are difficult fights and you're going to need a powerful Digimon to handle them.
At this point in the game you should have a good grasp on raising a Digimon and how it's done, if you're still having issues I would recommend my How To Raise A Digimon Guide. That will hold your hand and show you multiple ways to evolve into an Ultimate Digimon.
For the most part your gameplay loop is going to be spending time raising a Digimon at the gym until it becomes a Champion. Then you'll explore with your Champion while also training to raise stats whenever you can to reach Ultimate. Once you get an Ultimate Digimon you'll have 4 - 6 ingame days typically to explore and do things until your Digimon dies and you must start over.
In order to maximize your time spent, you'll want to focus on tasks that require an Ultimate Digimon when you get one. Things like beating the final dungeon, Angemon in Freezeland, Metal Greymon in Grey Lord's Mansion, Etemon in Native Forest, Piximon in Tropical Jungle and a few more all should be done with Ultimate Digimon for the smoothest experience.
Other things, like hunting down Nanimon, upgrading the training gym and much of the stuff we talked about in Chapter 1 - all can be done with a more basic Digimon. While we're on the topic of Nanimon, we mentioned the first half of the Key Chain earlier - when you find every location with Nanimon you'll be able to upgrade that Key Chain yet again. This will add another 10 items that you can carry.
You can learn more about all the locations Nanimon is found by checking out my Nanimon Recruitment Guide. Nanimon will always appear in locations that had "story elements", once you complete the story at that location you'll return to find Nanimon hanging out.
Now that we are in the final portion of this game, you have a few more zones to explore for Recruitable Digimon. Below you'll find a list of the remaining zones in this game that I didn't put on the previous page. The two at the bottom were on the previous page, I am just bringing them up again because the Ultimate Digimon at those locations may have been too hard for you to recruit previously.
Beetle Land Recruitable Digimon
Factorial Town Recruitable Digimon
Mount Infinity Recruitable Digimon
Freezeland (Angemon) Recruitable Digimon
Overdell (Metal Greymon) Recruitable Digimon
The final dungeon of Digimon World 1 is called Mount Infinity and it's going to be a real challenge for you if you have a weaker Digimon. In order to unlock Mount Infinity you will first need to recruit Airdramon, he is found in File City and will only attack you after reaching 50 Prosperity Points.
Defeating Airdramon will unlock Mount Infinity, you can access this location by going through the cave entrance in the northern portion of File City. Remember that waterfall that's been blocking off the cave for the entire game? It's gone now and you can enter.
Mount Infinity is a battle of attrition, that's the real difficulty of this dungeon. There are a lot of Digimon that block your way and that can run into you to trigger battles and the more battles you fight the more items you consume. I would recommend doing this dungeon in two or three different adventures. The first difficult Digimon to block your route forward will be Devimon, a few floors above him you'll find Metal Greymon.
Once you reach Metal Greymon you are one room away from the final boss. Normally I would recommend you push through to reach Metal Greymon your first go and then exit the dungeon to get more items and rest up. When you're confident you can handle the final boss, return and go through the entire dungeon again until you reach Analogman (pictured below).
Final Boss & Epilogue
Analogman is the primary antagonist of the game, there will be some dialogue when you meet him after which he'll summon MachineDramon. This is a Mega level Digimon so you'll need to be very prepared to beat him. I'd recommend bringing many items and an Ultimate Digimon at minimum.
Like with most things in this game, spamming item use will win the fight at the end of the day... but it would help you a lot if you had a good Digimon with a good finishing move (unlike the Digimon I had). Once you beat Analogman you will get the ending cutscene and the end credit roll.
You will be asked to save your game, which you should if you would like to continue playing. Beating the game unlocks the final Digimon that you can recruit, Digitamamon. To get this Digimon you'll need to make your way back through the entirety of Mount Infinity. You'll find an egg in the boss room which will unlock this Digimon.
There is also a bit more optional content for you and a few tough fights if you're interested. If you try and visit the Ice Sanctuary in Freezeland, Dark Lord Mansion in Overdell or the Ogre Fortress you'll be thrown into an area called the Back Dimension.
Back Dimension is a short dungeon that looks just like Mount Infinity, once you clear the dungeon you'll be spit out in an area with Analogman (pictured below). Analogman will be protected with a powerful Digimon whom you'll have to fight and defeat. Beating this Digimon will free one of three other Digimon, Muchomon, Soulmon or Yuki Agumon. From my understanding you won't be given any Prosperity Points for freeing these Digimon and they serve no real purpose. They more or less exist to give us extra content to do.
It's up to you if you'd like to continue playing the game once you have beaten it. The only thing(s) left for you to do are the Back Dimension and recruiting all of the Digimon.