Here are but a few of the many uses of the murderknife that make it an essential tool in any elf's life.
1. Throwing at the unarmed and helpless as they have their backs turned, pleading for you to not do what you're about to do.
2. Blood magic. Also handy for shanking, as it is all about the thug life.
3. Using it in combat? Like, as your method of fighting? I don't get that.
Anyway, somehow I couldn't stick to just one elf in DA:I, so you get the Lava Lamp twins. I'm pretty sure Brian's the Actual Inquisitor and Gilliam is the twin brother who always stays at eir side, but also spends a lot of time menacing Solas.