Mid-game Oriented Spectre
By at least theres kpop
NOTE: With 6.77c, Tranquils are getting nerfed. You're more vulnerable to ganks and your mobility in midgame fights is worse. Consider an early transition to treads unless you really need the regen.
A somewhat alternative take on Spectre, opting for a quickly maxed Desolate to allow her to be a very strong mid-game ganker that transitions well into a traditional carry role.
You will want to pair Spectre with 1 or 2 supports in your safe lane, preferably against a solo hero, as she still requires a decent amount of farm to hit her peak early. Once she hits level 7, she can be very aggressive with maxed Desolate. If you're absolutely never going to take advantage of that and need the extra survivability/slow, you can max Dagger or Dispersion, but your mid-game damage will suffer pretty heavily.
Haunt should be used primarily as a tool to allow you to farm in a lane far from your team while still being able to join a teamfight at a moment's notice.