Yu-Gi-Oh! Duel Monsters 4: Kaiba Deck/Tutorials

Text boxes in battle

Usually you'll be outside of Bank 06, since you'll be mostly calling these for card effects and lingering effects such as Swords of Revealing Light.
So do a rst 08 to Bank 06 pointer grabbing the at 6:400B, with the textbox ID in accumulator as the parameter.

3E 13            ld   a,13        ;0x13 is Stop Defense textbox
CF               rst  08
=> 0B 06                          ;Display text box

The parameter you send in accumulator is also used to retrieve up to 3 card_ids stored in three arrays at 6:41F3, used by display_textbox_func at 6:41B4.
You can display these card_id names in your textboxes using the special character codes (in DM3, these are 0xB5 to 0xB8, but it might be different in DM4, I will check).