All Bosses except X boss

This is a list of whether it is currently possible to skip killing one boss but still being able to kill all 25 other bosses.

All Bosses except Asylum Demon: Possible
All Bosses except Taurus Demon: Possible
All Bosses except Gargoyles: Possible
All Bosses except Quelaag: Possible
All Bosses except Iron Golem: -
All Bosses except O&S: -
All Bosses except Seath: Possible (with Warp Glitch)
All Bosses except Sif: -
All Bosses except Four Kings: Possible (with Warp Glitch)
All Bosses except Butterfly: Possible
All Bosses except Pinwheel: Possible (with Warp Glitch)
All Bosses except Nito: Possible (with Warp Glitch)
All Bosses except Guardian: -
All Bosses except Artorias: Possible
All Bosses except Manus: Possible
All Bosses except Kalameet: Possible
All Bosses except Stray Demon: Possible
All Bosses except Priscilla: Possible
All Bosses except Gwyndolin: Possible
All Bosses except Capra Demon: Possible
All Bosses except Gaping Dragon: Possible
All Bosses except Ceaseless: Possible
All Bosses except Firesage: Possible
All Bosses except Centipede Demon: Possible
All Bosses except Bed of Chaos: Possible (with Warp Glitch)
All Bosses except Gwyn: Possible (but can't trigger ending)