Arcbound Overseer [Darksteel] Phyrexian Zombie Assassin you may put a feather

you may put a feather counter on target creature

put a +1/+1 counter on Ob Nixilis

Must these roles be mutually exclusive

When Avatar of Discord enters the battlefield

Phasing (This phases in or out before you untap during each of your untap steps

Arcbound Overseer [Darksteel] Phyrexian Zombie Assassin you may put a featherSet: Darksteel Type: Artifact Creature Golem Rarity: Rare Cost: {8} At the beginning of your upkeep, put a +1 +1 counter on each creature with modular you control. Modular 6 (This creature enters the battlefield with six +1 +1 counters on it. When it dies, you may put its +1 +1 counters on target artifact creature.)