[Gredival]

In my opinion, for offhands Triplus is king. Rapidus Sax was tested to be the best offhand for Mandau before Heroes was released. Triplus vs. Sax is analogous to Blau vs. Sirocco, in which Blau won. Transitivity holds that Triplus beats Sax. I treat 3% 3A and 3% damage to 3A as a push against 1% Haste and 12 accuracy.

Twilight is designed as a mainhand and it adapts poorly as an offhand due to its dmg/delay. It is a decent mainhand, but if the question at hand is what do I use with Twashtar the answer is Triplus.

Should you get Twilight? That depends if it's "worth it" for you keeping in mind the fact that I don't think you should be offhanding it once you finish Twashtar. I personally would not be dumping cruor to brew Shinryu just for the Knife. But if you're going for Helm/Mail already and you got a chance to pick it up, it's definitely not a bad hold-over.

@Sham

The issue is a translation error. Tiger did testing and came to a conclusion about a 50% cap because he was assuming two Atmas were equal because they were both listed as Minor. However one Atma was really a major (revealed because it's listed as Major in different languages)

[IoriYagami]

Thanks for the input, Gentlemen. I guess I can put my Brews to better use, like +2 Item Nms

[TigerWolf]

So if I were to mainhand Twilight Knife, what would the optimum (or simply a good option) offhand dagger be for it?

[Gredival]

Triplus.