Her NP gain is mediocre, making it difficult for her to get that first NP off without support Servants or CEs. However, outside of her main niche as a farmer or in specific challenge quests, Mordred struggles to perform.
She also has fairly good durability, due to a high HP pool, and Secret of Pedigree offering her a three turn defensive boost along with a debuff cleanse. Against Altria type enemies, her damage is further magnified thanks to a super effective modifier on her Noble Phantasm overcharge. When she uses Mana Burst thereafter, she can deal major damage to her opponents with Clarent Blood Arthur.
With a 30% charge on Secret of Pedigree, she is quite capable of filling her NP gauge with proper support. Mordred primarily shines as a farming servant capable of clearing waves with ease. With a powerful Buster AoE Noble Phantasm, she will make all Altria type enemies quiver in their boots. With only one goal on her mind, Mordred swings her sword doing all she can to destroy her mortal enemy: her father Altria.