The document will guide you to get and reinsert the sprites and font (for a gb/gbc) from scratch, using a
GBC game as an example. However, many of the technics, procedures and knowledge involved may be and are probably used in other game console/hardware.
For this document/tutorial, you will be required to have and use the following tools.
Windhex, https://www.romhacking.net/utilities/291/
Game’s ROM: Kikansha Thomas – Sodor-tou no Nakamatachi (J) [C][!]
BGB emulator, https://bgb.bircd.org/
Tile molester, https://www.romhacking.net/utilities/109/
Staff/Credits:
Guidance and explanations: 342, Bootleg Porygon, zlago, Abridgewater, 256, vinheim3
File download: