Yeah, Jamison's DnB is something I'm also a fan of. I've been trying to hit that style myself, but I can't make it as good. Besides suggesting you have a look at my remixing guide (it's in my sig) for more general remixing advice, I've got little to say about the production side of DnB. So let's talk sources instead.
The most versatile sources tend to be the rather simple ones. Koji Kondo's music is often this, and NES- and SNES-era music is often this. Ironically, the Super Mario Bros theme is _not_. I got started on Super Metroid, Red Brinstar in particular, and I've got a DnB mix of it I'm working on (and failing to be satisfied with the mix). It's a source with a simple backing pattern that can be used in different ways, and a few lead melodies that play over it. Another commonly remixed track with similar qualities is Corridors of Time from Chrono Trigger, also with a simple backing pattern and a lead on top.
The benefit of using sources like this is that the backing pattern is often distinct enough to use to build the rhythm of the track with, along with the drums, but simple enough that you can do a lot with the bass things underneath (Ekaj's take on Red Brinstar, for example, has a great bass sequence).
The melody of course has to fit the mood of the genre, or be malleable enough to work there. Sometimes that means taking a melody and putting it in a different mode or scale. Breaking the rhythm of a melody and adapting it to a different rhythm means you have to figure out what the important notes of it are, and how to time those to the new rhythm. This is more art than science, and one of those "I know it when I hear it" things. I encourage you to experiment with this. For a take on melodies, I suggest you look at what WillRock did with an upbeat, major key Pokémon track. Both Will and I have a tendency to mess with melodies; my approach tends to be to cut them into tiny pieces and put those pieces to new uses, while Will tends to jump around chords and modes to adapt the melody to new things. Either approach could work for DnB.
I suggest you download the chiptune archives from ocr or other sources and listen for interesting sources. What you're looking for are tracks that have elements that could be adapted to DnB. Naturally, there's nothing magical about chiptunes that makes them better suited for this than any other kind of music, but the melodies are a lot more accessible than in non-chiptune compositions, and there's insane amounts of chiptunes to examine. If you're less inclined to look for music yourself, go on YouTube and search for people's favorite VGM lists, and listen for elements that you can use. Once you find something, have a closer look at that game's soundtrack and see what you find.