no attack or block for opponents creatures

Players can't gain life. Damage can't be prevented. All damage is dealt as though its source had wither. (A source with wither deals damage to creatures in the form of -1/-1 counters.)

Flying Wither (This deals damage to creatures in the form of -1/-1 counters.) Creatures your opponents control with counters on them can't attack or block.

Flying : This creature deals 1 damage to target creature defending player controls. Activate only if this creature is attacking.