Elsirelle is a time-limited water bruiser that deals magic damage. She can be surprisingly tanky since she has quite a number of defensive skills to be a physical wall. Her main damage spell is a water version of Law of Geoabsorption from Louelle, a strike type attack with a self-heal and can reduce counter chance by 100 at EX, effectively shutting down strong counter abilities like Yuna's Aeon Bond.
Since she's new, it's unsure how effective she is at handling both roles at the same time since the skills are separated, but her EX 120 ability is very powerful and could make her tanky without using her other DEF buffs. However, there are a couple of other potential issues with her kit.
Hate increasing skill is Taunting Blade, which will deal very little damage since it scales with ATK.
Might have to choose a role to focus on, and it starts with the passives and sub-job instead of during the fight.
Many of her skills have a casting time, and her Law of Speedreading is on main job sub-job.
Effective against King Mont in PvP, but no answer to magic attackers.