In His Shadow
House rules for Felicity March.
As written, Obtenebration 4 turns you into a tentacle monster, lets you see perfectly in complete darkness, makes you much scarier, and gives you four six foot long tentacles of darkness extending from your body. What it doesn’t do is tell you what to do with those tentacles.
The tentacles have Strength and Dex equal to the user’s stats, and also their Potence and Fortitude if any. As the book describes them, they enable a second attack each round once summoned, in addition to the other effects (fear, Intimidation +3 dice, -2 to Stamina and soak for those nearby, see in pitch darkness).
So really not so much house rules as reading the rules that exist more carefully.