Yeah, although relatively straightforward, Cu/Scath also gave me the most close call battle so far.
Berserker I dealt with after losing only 3 servants, and this was before I got a single copy of the Bride Umu CE. Assassins I lost only Mash, thanks to my 10/10/10 Amakusa with MLB Bride Umu CE ploughing through them like a tank, despite only using Iri as my healer because I never really got around to leveling up Medea Lily.
But Cu/Scath? Worried too much about Cu's evade spamming and accidentally killed him too quickly, and was down to 2 servants with less than 2k HP each when I took her down (though one of them was OG Umu and her Thrice Setting Sun, so in reality I still had some leeway).