After each level, this code is executed:
Language: asm
8F63: 21 5C 72 LD HL, 725Ch AF:FFAC BC:6000 DE:0000 HL:702C IX:9139 IY:C1DC SP:73FF cnP3h5zSe
8F66: 3A 61 72 LD A, (7261h) AF:FFAC BC:6000 DE:0000 HL:725C IX:9139 IY:C1DC SP:73FF cnP3h5zSe
8F69: 06 00 LD B, 00h AF:00AC BC:6000 DE:0000 HL:725C IX:9139 IY:C1DC SP:73FF cnP3h5zSe
8F6B: 4F LD C, A AF:00AC BC:0000 DE:0000 HL:725C IX:9139 IY:C1DC SP:73FF cnP3h5zSe
8F6C: 09 ADD HL, BC AF:00AC BC:0000 DE:0000 HL:725C IX:9139 IY:C1DC SP:73FF cnP3h5zSe
8F6D: 34 INC (HL) AF:00A4 BC:0000 DE:0000 HL:725C IX:9139 IY:C1DC SP:73FF cnP-h5zSe
8F6E: 7E LD A, (HL) AF:0008 BC:0000 DE:0000 HL:725C IX:9139 IY:C1DC SP:73FF cnp3h-zse
8F6F: FE 0B CP 0Bh AF:0B08 BC:0000 DE:0000 HL:725C IX:9139 IY:C1DC SP:73FF cnp3h-zse
8F71: DA 77 8F JP C, 8F77h AF:0B4A BC:0000 DE:0000 HL:725C IX:9139 IY:C1DC SP:73FF cNp3h-Zse
8F74: 3E 00 LD A, 00h AF:0B4A BC:0000 DE:0000 HL:725C IX:9139 IY:C1DC SP:73FF cNp3h-Zse
8F76: 77 LD (HL), A AF:004A BC:0000 DE:0000 HL:725C IX:9139 IY:C1DC SP:73FF cNp3h-Zse
8F77: C3 44 8F JP 8F44h AF:004A BC:0000 DE:0000 HL:725C IX:9139 IY:C1DC SP:73FF cNp3h-Zse
$725C is current level, it's loaded to register HL, incremented, compared to 11 (levels start with 0, so last level is 10). If it is 11 now, reset it to 0 and resume execution as usual ($8F44).