I've tried different builds with Abaddon and the full support build is the best way to go.
This build focuses purely on Mist Coil heal&damage and Apoc Shield to protect yourself and your allies to keep them in team fights longer.
Save your Apoc shield until an ally gets debuffed then hit them with it. itll remove most negative effects
Harass your enemies using mist coil instead of melee damage. Unless its to saved a ranged ally from death.
When enemies are low enough hit points, use mist coil on them to get last hit.
Also, when Borrowed time kicks in, use Mist Coil immediatley on friend or foe doesnt matter, this will heal you and damage an enemy or heal an ally.