While you are free to ask you are unlikely to find a straight title screen editor -- Kirby has never been the most popular game to hack, not to mention while title screens are popular enough to edit* you tend not to see them made for anything other than pokemon.
*others playing along at home I know we don't see them discussed around here very often (and it we ignore the pokemon monster editor and help with last bit of translation set then far fewer still) but there is a reason there is a decade+ old thread over on romhacking.net ( http://www.romhacking.net/forum/index.php?topic=10334.0 ) with about 1000 solid replies and 400000+ views, on a site where 10 replies and 2000 views is more normal, and usually forgotten in a week saving when someone else stumbles upon it years later)
Anyway had a look at about 21 seconds into
That looks like fairly standard 2d animations to me (being on the DS we have seen 3d used for such things before). I doubt the press start stuff is a font so probably also going to be 2d pictures, though I don't know if the repeated characters will be repeated in a tile map or if they will be just one set of pictures in a file. I don't have the game in front of me right now to pull apart and figure out which file it is in either. I would probably start by looking at file names, directory names, extensions and file sizes to either eliminate things or try to confirm it. After that I would have a look with in a tile editor in the various modes available (GBA 4bpp and GBA8bpp if you are going with crystaltile2) and either direct it by files; if you open it in CT2 and click the DS icon to bring up the ROM contents window you can double click to set the hex editor or tile viewer on that location, and if it is one of the formats it knows you can right click on the contents window and it should have options to force it to load as that file (you might need to do more than one to handle the graphics, tile map and palette), speaking of palettes then CT2 in the hex window can be told to interpret the following however many bytes as new palette if you want it to. Many of the other all in one programs like tinke and maybe MKDS course modifier could also be of use here.
vx is a video format (also seen in MODS, mobiclip and actimagine I think). I did watch the video above and look to see if it finished on that but no it was a fade to white before returning with the menu. We tend not to see interactive videos on the DS either.
Names, sizes, extensions as well as elimination based on those three are but one thing, frequently powerful but still just one thing.
Brute force - load it up and press page down a lot in each graphics mode for a few sizes. Might pop out at you during that.
Back search the ROM for the data from VRAM.
Some kind of file elimination. Make a ROM and remove whatever you think you want to from it, rebuild and run it in an emulator -- if it makes it to the title screen (probably going to need the ARM binaries, overlays, the intro video and maybe sound) then the file you want is in whatever remains of the game.
Corruption. Instead of eliminating files you edit them. If it appears but is corrupted then you have your winner.
.bin can be anything arm9.bin is the main binary the DS runs (and could house the title screen), arm7.bin in commercial games is a helper binary to handle some aspects of the hardware (you can swap them between games of similar vintage or just before and after most of the time they have so little unique to them), and things in the overlay folder are like the arm9 but swapped in and out of memory (they too could possibly contain the title screen, some games even stuff everything into ridiculous numbers of overlays). Ignoring the header and whatnot stuff in the main directory along with the arm9.bin then the other main .bin of note usually gets called utility.bin and is one of the ways download play works, speaking of which
.srl is quite often the download play (it is basically another DS ROM, opened with all the same programs) but I have seen it function as another aspect of the ROM before.
.vx I already mentioned is video files.
.sdat if there is one (would be surprised if not) is the sound for the game.
As for corruption then varies with what you need. Some people will copy and paste other parts of the ROM, some people will use a hex editor, some people might need to corrupt the file but only within certain ranges (you might well have had cheats in the past say don't put this value over 99 or it will crash, same idea here). There are tools though that will replace the contents of a file, or section thereof, with random junk though. http://www.romhacking.net/?page=uti...&perpage=20&title=&desc=corrupt&utilsearch=Go should have a few if your hex editor selection or own programming options don't do it for you.
Before jumping to corruption though I would do both ROM shrinking (maybe also run everything through decompression tools - https://gbatemp.net/download/cues-gba-ds-compressors.33556/ ) and opening in a tile editor to press page down a lot, repeating with it set with the common GBA 4bpp, 8bpp and custom widths for both of those. Also finding it in VRAM (desmume and no$gba should be able to tell you where it is in VRAM with their VRAM viewers) and searching for the same data or chunks thereof in the ROM/decompressed files.