Agreed. DO NOT kill Ostrava! Even if you don't care about the Pure clearstone, you will care about a - 30% world tendency, actually getting you to -60% assuming you died from Vanguard in the tutorial.
Just keep a close eye on him, especially in 1-4 below the blue dragon that he dies and becomes a black phantom, get the Masaulem Key from him.
As for the red-eyed knights, avoid them at all costs, AT LEAST until you have found the Thief's Ring and you can dodge all of his attacks. Blue-eyed knights are mostly recommended though, especially for melee focused characters.
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