It is worth pointing out that a ring that gives a mana discount for revealing an enchantment does credit the mage, even if a familiar cast it.
If a Warlock is using Sersirex (an imp familiar who can cast curses) and Ring of Curses, Sersirex pays the full cost of 2 mana to lay the curse down, but once it hits the table it becomes an object owned/controlled by the Warlock and thus his Ring of Curses does discount the cost to reveal it.