The Assassin Abyss Sphere
As noted already, I still think the number of shadows this permits should be lowered by 1 and that abyss blink should be removed and replaced. The question though I ask myself is what to replace the latter with that won't be too op and yet useful (and hopefully unique to the Assassin). So I'll throw out the following choices. As per usual, you're all welcome to throw in your own choices.
1) As mentioned above with possibly making the Valkyrie more survivable, consider doing the same for the Assassin's shadows instead of increasing their numbers.
2) Increase damage reduction (perhaps only by 5%) for the character. I'm sure this will be wanted for most Assassins who want to dual wield.
3) Have some kind of modifier that will help the Martial Arts build (kick damage perhaps) assuming no other items or skills will be modded to help that build in the next ladder.