It turns out that the new Phantom Lancer is still pretty broken! I played him again in a low party MMR game, and he got slightly buffed in the last patch so he's even better.
Now Skadi and Diffusal blade stack, so your primary hero still gets the skadi slow as well as the Diffusal burn on the target that you're attacking(but it's a very minor buff).
When playing the carry role, you can build a Aquilla and treads and afterwards grab a diffusal blade to massively increase the damage your illusions do(about 3-4x more damage if your opponents have mana).
After diffusal, you can either grab a manta style or skadi, and continue chasing down opponents.