Use White Mask Varre’s questline
Defeat Godrick the Grafted
Speak to Varre at the Rose Church in Liurnia
Use the Festering Bloody Fingers he gives you to invade other players three times
Return to Varre and accept the Lord of Blood’s Favor
Soak the cloth in the blood of a maiden
Return to Varre again and receive the Pureblood Knight’s Medal
Use the Pureblood Knight’s Medal to teleport directly to Mohgwyn Palace
Alternative route
Use the Consecrated Snowfield teleporter portal
Reach the portal in the western Consecrated Snowfield
Enter the portal to arrive in Mohgwyn Palace