Abyss Mysticism
Availability
As An In-Clan Discipline: N/A. As An Out-Of-Clan Discipline: Lasombra.
Please note that Mentor cannot be used to buy Abyss Mysticism rituals but they can be used to make quests about learning them more easy.
The Abyss Mysticism ritual selection is very, very small (about a tenth of the size as the Thaumaturgy ritual selection), meaning that if we were to use the "roll mentor to get this ritual" mechanic, then the act of learning most if not all of these rituals (which represent forbidden knowledge and unspeakable revelations) becomes trivialized into a few dice rolls that could have been compelling stories.
Path Selection
Abyss Mysticism is actually just a series of rituals, with no explicit path selection (the 'path' is Obtenebration). A vampire may learn any Abyss rituals equal to or less than than the lowest of their Obtenebration or Occult ratings. So, if you have Obtenebration 2, Occult 4, you may learn Rituals at levels 1 and 2. You'd have to have Obtenebration 4, Occult 4 to learn rituals at levels 3 and 4.
Ritual Selection
Each Abyss Mysticism ritual costs 3 times the ritual level in experience points to learn (thus 3, 6, 9, 12, 15). These rituals also cause permanent side effects associated with learning and using them: flaws obtained from these side effects are inevitable and do NOT reward the vampire with experience points. These flaws also can never be bought off. The side effects are described in the ritual descriptions.
Level One: Light Within Shadow (LOTC 126), Weight Of Shadows (ROTB 38)
Level Two: Comforting Darkness (LOTC 126), Feed The Darkness (ROTB 38)
Level Three: Claiming The Dark (LOTC 126), Abyssal Threads (ROTB 38)
Level Four: Vision Of Shadow (LOTC 126), Maw of Ahriman (ROTB 38)
Level Five: Commune With The Abyss (LOTC 127) Ahriman's Wight (ROTB 38)