Misty Trees - Digimon World 1
The Misty Trees is a small and annoying map, when you first arrive the entire area will be cloaked in fog. In order to remove this fog you'll need to speak with Cherrymon who is found at the border of Misty Trees and Toy Town. Before speaking with Cherrymon you'll first need to speak with ShogunGekomon in Geko Swamp. He will cast a spell on you that is required here.
When you are running through Misty Trees, going the 'wrong way' will put you back at the entrance (it is one of those puzzles~the lost woods). So, to reach Cherrymon enter Misty Trees from Geko Swamp and go east one screen and then north 3 screens. Alternatively, you could always just use a Save State on every screen and check the exits to see which one advances you and which one does not. I'd actually strongly recommend this esp when it comes to finding the next two Digimon.
After talking with Cherrymon you'll have a new training area as well, it lets you train Brains & MP.
Gabumon
Requirement: N/A
If you go north from the Geko Swamp entrance you will find Gabumon near a cliff. He is kind of hiding off screen to the left but you can see part of his body sticking out if you look carefully.
Kokatorimon
Requirement: Early morning hours, normally 4am until shortly after daybreak
From Geko Swamp go two screens east and search the northern part of this area. If it's during the right time you'll find Kokatorimon here who will join your city after a fight.