If anyone else has any issues with POW/Level codes, you might try this alternate way of doing it; just open the Memory Viewer and edit the values at these addresses (all 2 bytes unless stated otherwise):
233C420: Mario's Max HP, Current HP, POW, DEF, SPD, STA, Level (1 byte), EXP (3 bytes)
233C444: Luigi, same stats
233C468: Baby Mario
233C48C: Baby Luigi
For example, to input a value of 999 for Mario's POW and 100 for his level, change the two bytes at 233C424 to "E7 03" (3E7 = 999hex), and the one at 233C42C to "64" (64 = 100hex). This way you can change the values back whenever you need to for a tutorial or such.
233C420: Mario's Max HP, Current HP, POW, DEF, SPD, STA, Level (1 byte), EXP (3 bytes)
233C444: Luigi, same stats
233C468: Baby Mario
233C48C: Baby Luigi
For example, to input a value of 999 for Mario's POW and 100 for his level, change the two bytes at 233C424 to "E7 03" (3E7 = 999hex), and the one at 233C42C to "64" (64 = 100hex). This way you can change the values back whenever you need to for a tutorial or such.