You will always be automatically teleported to hell if your curse reaches 666 and you enter any room, cleared or not. Getting there isn't difficult if you try but beating it is very difficult, especially if you have any status effect that makes you auto concede, because the virtue loss is super high. I have only cleared it twice and once was with a bugged doll tf. I actually love how hard it is to clear, you have to plan your run completely around it and it's super enjoyable. The other cursed item that is super useful in hell is the cursed health pot, i can't remember its name but its the three use one that recharges and heals way more than it adds in curse, making it a very nice when your in a tight spot.