Don't go hollow, they said - but in Dark Souls 3, they change their tune.
Dark Souls 3: Dark Sigil and hollowing explained
In the world of Dark Souls, going hollow means losing the vestige of humanity as you succumb to the undead curse. Most humanoid enemies the player meets are hollows - barely more than aggressive, animated corpses.
In previous Dark Souls games, players went hollow when they died, resulting in lower health and the inability to summon co-op assistance, and they'd have to use a Humanity item in order to return to their normal form. This isn't the case in Dark Souls 3; players lose their Lord of Cinder form upon death, and must use an Ember to reclaim their fire, but do not go hollow.
Nevertheless you can go hollow, and it does have consequences. On this page we'll explain how hollowing works in Dark Souls 3.
How to go hollow: the Dark Sigil
Players will not go hollow until they are branded with the Dark Sigil. The Dark Sigil is a key item acquired from Yoel of Londor when the player accepts his offer to draw out their true power. See our NPC guide for information on how to recruit Yoel.
Once the player has a Dark Sigil, each death will add to their hollow level at a rate of one per Dark Sigil held. If you have one Dark Sigil, each death adds one to your hollow tally, and if you have two, it adds two levels - and so on.
Yoel offers up to five Dark Sigils, giving a free level up each time. Each of Yoel's five Dark Sigils is available only after reaching a certain level of hollowness. You'll need 16 hollowing to access all five free levels, and must achieve this before advancing the game too far as Yoel will die after a few bosses are defeated.
Hollowing caps out at 99.
Effects of being hollow
The most noticeable effect of hollowing is that the player takes on a corpse-like appearance. This visual effect grows more severe as the player goes more hollow. (Also, as of version 1.03, your shadow disappears when hollow - which is likely a bug.) This does not seem to have any effect on NPC interactions.
If you don't like the way your character looks when hollowed, you can purchase the Untrue Dark Ring from Yuria for 5,000 souls. It doesn't affect your hollow status, but makes your character look normal.
In terms of gameplay, if your hollowing level is above 15, weapons infused with a Hollow Gem will boost the layer's Luck attribute. A +10 Hollow weapon will give a +5 bonus to Luck, which can be doubled by dual-wielding to +10. This is very handy for farming items. You'll need to retrieve the Profaned Coal from Irithyll Dungeon before Andre will offer this upgrade.
Reversing and curing hollowing
There are no negative consequences to being hollow, but you can both wipe your current hollow tally and prevent yourself ever becoming hollow if you want to.
To reset your hollow tally to zero, purchase a Purging Stone from Yuria - or, if she is dead, from the Shrine Handmaid after turning in Yuria's Ashes.
To reset your hollow tally and prevent further hollowing altogether, you must cure the Dark Sigil. This will close off the third ending and cause Yuria to leave Firelink Shrine. To cure the Dark Sigil, you must retrieve the Fire Keeper's Soul from the tower behind Firelink Shrine. Curing the Dark Sigil becomes more expensive as the game progresses, so you will want to do it as early as possible.