I can see your SAW build working, however Tyrant's Monocle isn't as good as another Sorrowblade. He doesn't need Tension Bow because he is not a burst hero- rather he has some of the best damage sustain due to his Spin Up.

Koshka doesn't need Serpent Mask and it will do little good, since she does less than ideal weapon damage with those crystal items. Besides, Koshka will die in a fight if relying on lifesteal, her defenses are not good enough to support damage sustain.