f→f (same) y→i (y→i shift -8?) not consistent. Let’s check: f→f (0), y→i (y=25, i=9, diff -16 or +10 mod26), inconsistent.
Key “oxvpn”: length 5: d(3)-o(14)=15=p a(0)-x(23)=3=d n(13)-v(21)= -8=18=s l(11)-p(15)= -4=22=w w(22)-n(13)=9=j d(3)-o(14)=15=p → pdswjp no. danlwd Ox Vpn bray andrwyd fyltrshkn aw ayks wy py an
Try right shift: d → f a → s n → m l → ; (not likely) — fails. If fyltrshkn → “filtering”: f→f (same) y→i (y→i shift -8