I highly recommend that you max Moon Bind. It's quite useful in Myth since all of the mobs can be frozen.
Light of Purification should be kept at level one to remove curse ailments.
Maintaining MP is not an issue in Myth since Myth equips give copious amounts of Dexterity for lower CD, so you could rely on PoS and MP potions. Having said that, you could consider maxing Concentration and dropping Mana Recovery. For a larger mana pool, you could max MP Increase.
Light Shield is probably one of Eirs best skills. You're invincible from any attacks (as long as you don't attack) for a certain amount of time. It's really useful in tight situations, such as trying to reach a far portal safely that spawned in the Room of Ordeal at Myth II, as an example. I recommend keeping Light Shield at level two/three.
You could raise Moon Fog to level nine, since that's when it reaches its damage jump. One of the recent patches lowered the CD for Moon Fog, making it one of Eir's strongest attacks.
Self-Heal should be kept at level one to cancel spells.
I recommend Tears and Holy Spirit at level one. I usually use either of these prior to casting JoG in order to flinch the mobs.
You could keep prayer at level one for fake resurrection.
With the leftover five points, you could max RB JoG. If you have two pieces of the Ancient Elf Hero Set, you could cast normal JoG, and then cast RB JoG. Although it requires a large amount of mana, it does quite a lot of damage.
Lunia Skill Calculator(JP)