For others playing along that would be Adventure Time - Hey Ice King! Why'd You Steal Our Garbage! for the DS (there was only one game for the DS, several for the 3ds though).
While there are a few font formats that are known and with various levels of editor there are still just as many that use custom formats and you get to work it out if you want to play translator.
More annoying is I have seen several formats have completely custom tile sizes for every character in a font so it is not even a matter of finding out it is a custom size for all of them to set a tile editor to. Offhand I don't know what this would be but given they went to the effort of using a non standard format for the audio (I remember ripping the title theme once for someone) I would not be surprised at all to see something quite custom here.
Watching the video
Looks like a variable width font at least (the i characters being far thinner than others), though that can still be defined in software and all the tiles it is stored in end up the same size.
At the same time also only a single colour so it might be one of those 1bpp things if you are unlucky (or possibly lucky).
Step one would be to find the font used in the game; sometimes games will have various fonts only used for end credits, error messages or something and it really sucks to spend 5 hours pulling something apart only to find the devs left it in the game from an earlier build. If you think it is that one give it a bit of corruption in a hex editor (probably a bit into the file so as not to mess with headers).
ḯ̵͙͓̤̱̺̮̫̰̗͜f̵̥̠̗̭̖͉͈̦͗́̀͆̆̀ ̷̧̙͉͓̓̍̚ͅÿ̸̛̖̞̰́́̾̌̐̍̍̋̃͗̐͠o̶͔̬̖̼̗͕̯̞̜̍̐̈́̒̏͑͌̔̎ứ̵̤̹͕̤̼̯̠͍̻͒̎ͅr̴̹͙̝̹͛͛̾̓̾̆͐͑̕ ̶̢̜͍͊̆̉̂͝t̵͔͎̮̂̋̇̽͒͛e̵̟̗̓x̷̞̤͎͎͍̋̾̇̿̕͝t̵͇̾̀̔̈́̕ ̶̯̤̆l̵͈̫͓̻̼̬̟̫͈͙̞͔̜̋̚͝ò̴̢̡̜̲̼̜̗̞͙̟̙̉͠o̴̲͈͆̀̎̾ḳ̴͎̀͊̌̑̚͘s̵̨̛̞̲͎͔͔̠̩̓̈̃̆̀͋͑͘͜ ̴̛̞̭̗̙̝̝͙̰̙̣̑ͅl̵̻͙̇́̉̈͐͗̿̏̒͊̇͠i̷̧͔̙͔̠̰̻̍́͒̏͊̾k̵͉̜̳͓̫̲̮̻͇̤͙͉̓̈̒̂͌́͠͠e̸̢̨͙̮͍̳̘̦͎̍͂̏͗̈̀̈́̅ ̶̡̘̳͖̦̯̫̼͈̯͓́̂́̈́͋͐̊͐̉͝ͅt̶̡͍̗̻̘͔̩͛͛̀̀̄͠ẖ̶̜͍͎̫̭̥͍͎͕͉͆́̅ͅi̷̙̿ś̸̲̻̙̋͊̀̑͂́̆ when you are done editing you know you have the font. Now you get to figure out how it works.
Two main approaches for me
1) Brute force
Tiledggd and crystaltile2 are my preferred editors for narrowing on in what the format is (most characters are some value between 3x5 and 16x16 pixels, the tile viewer in an emulator will also help in this).
https://www.romhacking.net/utilities/818/
https://www.romhacking.net/utilities/646/
2) You look at the format
Earlier I mentioned about a game having each character be a custom size, and quite possibly different to the last. The thing about that is that it has to mention that somewhere in the game else the game would not know how to handle it. Most times this data will be in the font file along with the graphical parts of the font, usually at the start but might be before each individual character.
