FADE

Aura of Health: Grants targeted ally HP Regen for x full turns and cures Bleed. Restores 2 MP to Eldin.
0MP
This Skill is vital to survival early on, but should stay relevant throughout the entire game thanks to its zero MP cost to cast. Is more effective when used in battles with a good number of enemies on the field.

Shine: Deals above moderate Light damage to target foe.
12MP
While it doesn't have the chance to inflict conditions, like the versions Roth and his friends have, it does deal more raw damage.

Mystical Light: Restores some of Eldin's MP and cures Burn.
6MP
A very good option to allow Eldin to use more Skills more frequently. Manage her MP well using this Skill, and she can continuously blast enemies with Shine for high amounts of damage.

Glimmering Ray: Deals more damage to target foe when there are less foes on the battlefield.
15MP
Hits like a nuke with only 1 enemy on the field, definitely worth using over Shine if she has the MP for it. Has about the same effectiveness with 3 enemies around, compared to Shine.

Pure Wish: Restores x% of target ally's HP at the end of the next turn.
10MP
Unlocks: Zealous Spirit: Heals x% more to ally targeted by Pure Wish on the previous turn.
0MP
A decent burst heal, at the cost of being delayed by a turn. Its effect can be strengthened for free, but will cost Eldin another turn. Especially effective when you know target ally is going to be hit by a lot of damage a turn in advance.

Star Mines: Lays down a mine that has a chance of exploding at the end of each turn. Deals more damage with more mines on the field, up to a maximum of 5. Resets after exploding.
5MP
Eldin's best answer to dealing with groups of enemies. While an explosion after a few casts does a good amount of damage, unfortunately, Eldin has no way of controlling when the mines will explode. This might cause them to explode early on, for less damage than you were hoping for, or perhaps wait a few turns too long when the majority of enemies has already been wiped out.

Rain of Mercy: Restores 1MP to all allies at the end of every
turn for 5 turns.
5MP
A slow Skill at low cost with decent benefits. It's also Eldin's only option to provide MP regenerative support to her allies. Great to use in encounters when you're unsure what strategy to go for, and just taking it slow for a bit while slowly charging your party's MP.

Guardian Angel: Target ally that goes down while under this effect revives with 100%HP&MP. Can be used only once per encounter.
15MP
The only Skill in the game that'll allow you to bring back a downed ally. Can be used as a way to fully heal up an ally, but they'll need to go down first.

Chain of Life: Whenever target ally uses a Skill, restore 10% of that ally's and Eldin's HP. Can only be used once per encounter.
15MP
Eldin's 2nd Elite Skill, making you choose between this or Guardian Angel in every encounter. It's a great way to keep an ally (and Eldin herself) healthy without having to actively heal them, as long as they keep using Skills. Works especially great with the Auras at 0MP and Roth's Echoing Thunder, which only costs 5MP per use.

While Roth is the party's main support for MP regeneration, Eldin is the one taking care of the HP side of things. Eldin can still be a very powerful spellcaster that can deal lots of damage if you keep fuelling her MP.
Eldin's Skillset allows her to do pretty much anything you want, her main weakness lies in her stats, which are a little below that of the rest of the party members. Especially her HP stat makes her somewhat fragile, and she does require additional support if you want to play her primarily on the offensive.