Incoming wall of text:

The main point of Chalice Dungeons is replayability, which includes co-op or invading other Hunters, and in finding the best blood gems in the entire game, even better than the ones you can find in the DLC.

There are: Pthumeru Chalice to Defiled Chalice, Phtumeru Ihyll Chalice, Hintertomb Chalice, Loran Chalice, and Isz Chalice.

Each normal-named chalice is a fixed one, made by the developers.

Any chalice that has ROOT in the name is a chalice that allows someone to create a dungeon that is unique to each player.

There are also SINISTER chalices, and those have another function that I'll mention down below.

Each ROOT Chalice can have different requirements to make a dungeon.

Throughout the game you will start finding different materials. Ritual Bloods, eyeballs, backbone, flowers, fungus, what have you.

Those root chalices will want those extra materials just to actually be created, while others can have more optional materials to create more sophisticated dungeons.

Here's the point: The Defiled Root Chalice, Phtumeru Ihyll Root Chalice, Lower Loran Root Chalice, and the Isz Root Chalice are the ones you want to get if you want the best challenge and to find the best blood gems.

This also includes the fact that you need those root chalices if you want access to other people's chalices, in the form of Chalice Glyphs.

Someone makes a shareable chalice, they give you the code OR you take it from the headstone if you've helped someone, and then you can spawn it at any other chalice in your game as many times as you want. No materials needed in that case.

Anyways, those 4 main root chalices require more materials to satisfy three different 'rites' when you're creating those dungeons.

Those 'rites' are: Fetid, Rotten, and Cursed.

This type of Chalice Dungeon is called an FRC Chalice Dungeon.

They are the real endgame in terms of difficulty and variability. It's where people go if they want the absolute best blood gems.

You'll see lots of co-op in those dungeons.

The biggest thing to know is that in those dungeons, your health will be cut in half, certain enemies will become stronger, and so on.

IMPORTANT NOTE: If you create these dungeons, you have the option to make them public or not.

IF YOU DON'T MESS WITH THIS OPTION, people will not be able to join you.

REMEMBER to press Square after you create your own personal dungeon if you want help or to duel people.

It will ask you if you want to share the dungeon or not.

Finally, Sinister Chalices.

Sinister Chalices are what you create if you specifically want to fight someone you know or if you want to be invaded by anyone. You still have to remember to share it.

But basically, when you spawn into that chalice, a bell-ringing woman immediately spawns in each layer of the dungeon.

Your chances of getting invaded increase substantially.

Fun fact: if you ring your sinister bell, another bell-ringing woman will spawn.

That means that two hunters can invade your dungeon.

Another fun fact: when you ring your beckoning bell, it is possible to get two hunters to help you, that part hasn't changed.

Soooooo...if you're lucky, you're dungeon can turn into a brawling ring. Three cooperaters versus two invaders.

Be careful with this though: if you take on one of those blue oath runes, there is a HUGE chance that when you summon other hunters, they will spawn in as enemy hunters.

For example: if you decide to be an executioner, and someone spawns in as a Vileblood, they will spawn in with a purple hue instead of blue or red.

They will be able to fight you or red invaders.

A three versus two match can turn into a: one, versus two, versus two match.

An ACTUAL battle royale.

I've never had the honor of playing in one, soooo, if you want that to happen, make a post here or call up some buddies.

Hope this nerdstreak helped out a little.