I just have my fan-wielding Paladin use Reverse Cycle, then spam Forbearance until Knight Watch triggers. No need for Magic Mirror, since Malroth never uses spells. She's got enough HP to take a full C-c-cold Breath if he ever uses Disruptive Wave before it.
Actually, I think he is one of the more difficult ones. Most of the bosses are weak to an element they use but Malroth does not. He also does a fair amount of damage especially if he psyches up. Blinder also forces you to not have an accessory like higher critical chance or higher coup-de-grace chance.
He does have a throwaway ability in Fullheal, but it still heals him for a decent amount - probably heals the amount of damage by a level 99 gladiator with falcon slash and a falcon blade. He's probably only easier than Nokturnus, Estark, Dragonlord, and maybe Zoma although I think Malroth is harder than Zoma.