Calith

Calith suffers from both availability issues and being rather unremarkable. She is the only unit I considered for D tier; however, she is still usable. Designating her role as a Repulsor Shield or Ancient Writ bot is probably the best way to go with her.

At level 30, you generally have about 10 more levels to go. Unless you are favoring a character or farming a lot, You generally won't make it much past level 40 - MAYBE level 45. At this point in the game, look at the character's bases compared to the growth rates. For every 10% of a growth rate, just add 1 point and you'll have your level 40 endgame stats. 

Calith is an unfortunate unit. She comes so late into the game as a tier 2 class that you need to promote when you should pretty much already have your units you plan on using for the rest of the game at this point while not offering anything great. Her passive and personal skill come across as unsynergetic because one increases avoid while one increases defense; however, I like to think of it as a failsafe. That said, its still not great! For every 10 stacks of Blind (light/heavy/severe all seem to count) within 2 tiles she gets 1 extra defense and fortitude. So anywhere from 4-7 per enemy within 2 spaces of her (technically allies should count too). Its ok at best. 

Loremaster - This is probably her best class due to her just being unremarkable. You can run an offshoot version of her personal skill in The Breaker with Radiance Ring dealing some chip damage and 30 Light Blind. Your main focus in this class will be acting as a mana battery and reducing allies' mana costs. It is worth noting that Calith still does have decent enough bulk average speed and attack, she can safely enter combat and try to get some mana back after giving it to allies. 

Necromancer - Calith's mastery is not very high and is going to be burning through her mana to give it to her allies. With Necromancer, she can gain enough mana to be efficient at being a mana battery and also gains access to Animate. While there's not a whole lot that is special about this build, the true beauty is that it is efficient and doesn't take any resources. The Dauntless and Elemental Ring are near uncontested and while neither ring is great, they do offer some synergy with her kit. Dauntless offers a little damage reduction in the form of more bulk and Elemental Ring gives you 10 light block for every 50 mana you spend - which you should be doing a lot as a keen Necromancer with Animate, Phase, and Ancient Writ. 

Cosmician - Calith likes to take this class to make her feel like she's contributing more, when in reality, she's just taking resources from better units. With one of the few most precious rings in the game being Lava/Mystic/Heir Rings and the Inferno Ring, she can actually start to kill things on her own on occasion. Her primary role will still be that of a mana bot, but with Cosmician as her tier 3, she will at least give more mana as well - granted she's full HP. And hey, she can occasionally give your team a small heal.