(3)shadow piercer-increase number of targets, 75% chance of 10% heal
(5)aimed shot-dmg, 250% crit dmg, crit chance by 10% for 5 seconds, 15% armor reduction
(3)razor shield-duration, bleed damage
(3)shadow veil-duration, smoke bomb
in order of what I chose

When I had the heal skill I felt like I was more of a support character, helps with your survivability for sure but when I actually needed the health packs everyone else would take them. At lower levels I always ended up taking aggro even if I waited for warriors to charge a lot of warriors I ran with ended up running away to regen or waited til someone else took aggro/lead to die first. Personally for me shadow piercer heals me just enough to pop a potion or two if I really need it. The one thing I'm not so sure of about this build is the smoke bomb upgrade, unless you don't have the extra 3 sec upgrade it'd probably be viable but since things usually die before it actually explodes it's not all that useful. I still have yet to try out the whole 20% armor upgrade though that might have more utility than the bomb. Still curious about the trap too seems like maybe it'd be suited for soloing.