I think that the rest is drawn in the background etc.
If you examine it with the graphic editor, it may come out, but it has not been discovered yet.
Processing is executed by FE8U (0806fa84 SpecialBattleBackgoundChange)
It is an argument that passes here to the r1 argument, it changes as becoming the demon king or dragon.
However, details have not been analyzed yet.
08057724 4802 ldr r0, [pc, #0x8] # pointer:08057730 -> 02000000 (WRAM )
08057726 6800 ldr r0, [r0, #0x0] # pointer:02000000 (WRAM )
08057728 2101 mov r1, #0x1
0805772A F018 F9AB bl 0x0806fa84 //SpecialBattleBackgoundChange
0805772E E006 b 0x805773e
08057730 0000 0200 //LDRDATA
08057734 48A9 ldr r0, [pc, #0x2a4] # pointer:080579DC -> 02000000 (WRAM )
08057736 6800 ldr r0, [r0, #0x0] # pointer:02000000 (WRAM )
08057738 2102 mov r1, #0x2
0805773A F018 F9A3 bl 0x0806fa84 //SpecialBattleBackgoundChange