Best low-rarity assassin for Camelot?

Jing ke is good boss killer, serenity for debuf and cursed arm if you looking for more durable assassin

Sasaki and Jean Kay... Hard to choose. Sasaki skills all good but due to his super low rarity his stats is bad. Jing Ke is crit based assassin similar to Sasaki but with better stats. She lack of evade skill so you might want to prepare a support that can help with her survivality. Both already have strengthening quest that will increase their functionality. Damage wise I'll go Jing Ke. Fun wise I'll go Sasaki.

You might also want to considered the three Hassans. Curse Arm act similarly like OG Cu except for much lower stat than lancer due to his 1 star star. 100 face is kinda similar to emiya but her 2nd skill is chance based. She can also possible to loop her NP. Serenity is also quite good but with lower damage than 100 face. Her poison niche will get upgrade next year with skill strengthening and NP upgrade from interlude.

Fuuma Kotaro can act as support assassin and star generator( he can generate star almost as good as Jack). His skill can also help your main assassin survival with atk down and target able evade.

Jing Khe is better than Sasaki due to the stat difference.

But i would say that it's better to wait for Fuuma or Serenity.

Regend is IMO way better all around, provided you are willing to toss a few grails his way.His skillset is leaps and bounds above Jing Ke,and leads to some interesting solo potential.Just look at all the solos that people have been doing with him on Youtube and see for yourself.

AOE assassin is rare and Fuuma is one of your good AOE assassin along with Assassin Scathach.

Babylonia has multiple rider waves with huge HP and you can use Scat ass there to clear the waves easily and even use her as your daily farmer and taunter.
She's worth the investment.