Follow the code down from $8000 (RESET) to $805f, where there are a handful of subroutine jumps. One of those calls goes to $80b6:
Code:
P_80B6 ; [80B6]
lda Z_24
beq A_80BD
jmp J_8101 ; [8101]
A_80BD ; [80BD]
lda Z_25
jsr P_85B3 ; [85B3]
tax
!byte $82 ; illegal opcode
E_80C4 ; [80C4]
!byte $D4 ; .
E_80C5 ; [80C5]
!byte $9C ; .
E_80C6 ; [80C6]
ora Z_9D
!byte $1C ; illegal opcode
E_80C9 ; [80C9]
sta A_A9A3,X
cmp A_6D87,Y
txa
!byte $AF ; illegal opcode
E_80D1 ; [80D1]
!byte $89, $16, $AC, $4E, $AC, $6D, $AC ; ...N.m.
!byte $EF, $AC, $A3, $A9, $FC, $80, $62 ; ......b
!byte $A0, $D9, $87, $D9, $87, $C2, $84 ; .......
!byte $34, $88, $55, $B2, $81, $B2, $B6 ; 4.U....
!byte $B2, $CE, $B7, $17, $BA, $E6, $B7 ; .......
!byte $48, $83, $22, $81, $1F, $82, $27 ; H."...'
!byte $9A, $A9, $0A, $85, $25, $60 ; ....%`
J_8101 ; [8101]
lda Z_26
jsr P_85B3 ; [85B3]
!byte $92 ; illegal opcode
E_8107 ; [8107]
sty A_8CC8
!byte $13 ; illegal opcode
E_810B ; [810B]
sta A_8E1D
lsr Z_8E
!byte $5A ; illegal opcode
S_8111
@lidnariq, am I am looking at this code incorrectly? The CRC32 for the image I'm using is e2554e0a. I got the image form a large comprehensive NES ROM torrent, the file name is "Duck Hunt (VS).nes". The torrent includes just one other copy of Duck Hunt VS entitled "Duck Hunt (VS) [b1].nes". Its CRC32 is 8862afd7 but I notice there seems to be graphical corruption with the dog.