In the right team, Caster Marie can serve as an amazing support, bring crit stars and crit damage. While she brings a little damage to the table with her NP, it is not the focus. She is not the best servant at generating stars, but she can also absorb damage well.
Pros
Her Arts Centric deck makes her easy to pop into many teams.
Her kit synergizes well together (Crit support).
Has decent survivability with her skills.
Cons
Low damage.
Strategies & Tips
She is at home in a Arts crits team, and can serve as a buffer and star to the team. Using her NP to lead into other servant’s Arts cards can generate a large amount of gauge for the other servants in the team which helps recover after unleashing an NP barrage.
Noble Phantasm
Crystal Dress: Deals damage to all enemies, reduces their crit rate while also buffing Allies crit damage for 3 turns. Overall a good effect but somewhat reliant on luck to make use of the buff.
Star generation when combined with Marie is extremely good. Their buffs are also both support crits. His NP also brings healing and buffs to help bring Marie’s durability even higher. Overall they’re a very good combination.