Doppelganger (1) generates too strong images, can easily tank multiple tower hits in early game. (2) its animation is very misleading because the animation uses the hero model. It is problematic because hero is invulnerable while casting. My suggestion for this skill is backtrack to the previous animation and speed it up. Maybe add more clear destination animation.
Mortal Wounds in combination with Poison Nova: Poison Nova damage cannot kill targets, but Mortal Wounds buff may trigger cumulative damage over time and effectively kill. It may be a great combo, but I think it is more powerful than most of combinations, given the extremely big overall damage from Poison Nova.
Phase Shift lost most of its usefulness as it does not make model invisible.