Considering
also has Quintessence, the nymph entering the field immortal is unnecessary.
Turquoise Nymph is really a mono-Anubis, keep that in mind. It has better attack, same summoning cost, ability works in mono decks. Only real downside is the health, which given the easy Quintessence combo, should only be a problem when facing harmful shields.
I think it's fine the way it is. In fact, I wish I had one, I'd put it to good use. Yes, by the time you can play this you'd have been able to play 2-3 Quints, but you have to DRAW 2-3 Quints before you can play them. Once one of these is on the field, you can just keep on using it. Otherwise, what would be the point of people using Anubis to begin with?