3E Dmg (TarCurHP-1)

[3e]
0018a00c: 27bdffe8 addiu r29,r29,-0x0018    
0018a010: afbf0010 sw r31,0x0010(r29)       
0018a014: 0c0619bb jal 0x001866ec           -->Gravi2 Damage Routine Set HP damage = Target current HP -1
0018a018: 00000000 nop                      
0018a01c: 8fbf0010 lw r31,0x0010(r29)
0018a020: 27bd0018 addiu r29,r29,0x0018
0018a024: 03e00008 jr r31
0018a028: 00000000 nop

Return location

Battle.bin
0018b97c - Pre Formula Setup