Obfuscate ability is given to Wilhem after navigating Josef's Tunnels. Christof gets it after the encounter with Luther Black, after the party has left Stephensdom. Lily gets it after the Giovanni Stronghold is raided. Samuel starts with it. In modern times, this leaves only Pink to benefit from the Tome in the Setite Temple.
Nosferatu in the single player game all have varying levels of it, making more and more of their actions invisible. At the lower levels, the user can only be seen when moving. Nosferatu NPCs in single player, and Nosferatu and Malkavian NPCs and Player Characters in multiplayer start with this discipline
Whether or not an Obfuscate user remains hidden depends on their actions, and the level of Auspex used to detect them. Standing still is the most hidden, then moving; attacking in normal Redemption always reveals an obfuscated attacker. Low levels of Auspex will reveal low level Obfuscators even when standing, but only detect medium level Obfuscators when moving. There are some more complicated and possibly even bugged or random relationships between Auspex and Obfuscate, such as whether a cloaked enemy or character will reveal himself when Feeding or being Fed on by a character or NPC. Generally speaking, Serena does not need to spend more on Auspex to make it through the first Nosferatu dungeon, given a judicious abuse of Awe, nor does more really help, as she does not have Awe herself, so she can only attack the things she sees, or Feed on them if they are Awed by Christof or Wilhem
It is a fact: single invisible assassins in a group of visible compatriots defeats the damage prevention objective of Stealth, as the damage is then dealt to someone else. In fact, this goes some of the way towards forcing the enemy to adopt the superior tactic of Concentration of Fire. That is, attacking and therefore eliminating one single source of incoming damage at a time. There remains, of course, the tactical advantage of taking out a particularly dangerous target amongst the enemy group. However, this is less effective in Vampire than in other games, as there is no discernible advantage to attacking from behind in Redemption; in fact there is a handicap to the chance of hitting a target with its back to the attacker, if it is running away (and a better chance to hit a target that is moving across the attacker's attack radius)
The Cloak the Gathering skill removes the vulnerability of unstealthed party members. However, it is highly recommended that the party not evade battles with enemies; every enemy target left behind is XP lost, and the enemies that respawn are few, far between, and offer very little XP
The Within the Darkness mod attempted to address the problem of the weakness of stealth, but ended up creating an "I Win!" button; at five dots, with the WtD mod, enemies can not even see Obfuscated characters when they attack. The party becomes invincible, and the only challenge left is in things the player makes up for themselves, such as killing things as quickly as possible
This effect can be replicated for Christof or any multiplayer character by casting, only in this order, first Cloak the Gathering and then Cloak of Shadows. Cast the other way around, and the game checks to see if a stealth effect is in place when casting the other spell, and overwrites it. Instead, Cloak of Shadows stacks with Cloak the Gathering, and the levels of stealth are added together. Any values of the two that add up to six are undetectable by any enemy in the game.