I gestalted a Nymph with a Succubus. It's one of a few unique creatures in my campaign setting, result of decades long experiments by a powerful mage.
With this particular monster fusion it's essentially a Succubus plus Nymph abilities (because all the other stats are either the same, almost the same or the Succubus has better than the Nymph).
My question to you is: What additional CR would you give the Succubus for the Nymph abilities?