Here is a Pocket Guide for Omen to set up your game! Omen can counter all separate push hero,including Kilgroth,including Taara and others. Himself is hard to be countered by one single hero. He seems to be designed for the sole purpose of countering Superman.
Tips:
1. Hide in bushes and camp for weak heroes that are walking alone, pull them in with Death's Beckon and kill them with your ultimate.
2. Death's Beckon does not pull enemy heroes through walls.
3. Before engaging in a fight, stack up some Thirst points.
4. His passive increases his movement speed, attack speed,
deals true damage and also reduce cool-down on his Death's
Beckon and Untouchable.
5. His third normal attack also deals 50% extra damage.
6. Omen's Untouchable can also be used to slow enemies that
are far away to stop them from chasing up to him.
7. Learn first skill at level 1. This will help you to gather waves
together and will increase melee's wave-clear ability rapidly.
8. Don't use second skill to get into enemy team. It should be
used when being targeted, usually used when Omen already
gets into enemy team and uses his ult successfully.
Passive:
Every time Omen hits an enemy with a normal attack, he gains one Thirst point. After reaching five points, Omen increases his movement speed by 60 and his attack speed by 25% for 5 seconds. His strengthened Normal attack will also deal 60 true damage and reduce the cool-down for Death's Beckon and Untouchable by 1 second.
Omen's third normal attack triggers a second hit that deals 50% damage. The counter is reset after reaching 5 points of Thirst and after coming of Thirst.
Omen passive can reduce his skil cooldown.In other words, Omen can transfer attack speed into CDR.
True damage occupies Omen damage about 1/3. He does not need armor pierce, unless facing a very tanky team.
Best backline protection in a teamfight is a smart Omen!
Flicker is essential. Flicker + ult = wrecked squishy. And save your Untouchable when the enemy is going to use a burst skill, like Valhein or Murad's ultimates.
Ability Combo: Death’s Embrace(Ult) + Untouchable(B) + Death’s Beckon(A)

Tips:
1. Hide in bushes and camp for weak heroes that are walking alone, pull them in with Death's Beckon and kill them with your ultimate.
2. Death's Beckon does not pull enemy heroes through walls.
3. Before engaging in a fight, stack up some Thirst points.
4. His passive increases his movement speed, attack speed,
deals true damage and also reduce cool-down on his Death's
Beckon and Untouchable.
5. His third normal attack also deals 50% extra damage.
6. Omen's Untouchable can also be used to slow enemies that
are far away to stop them from chasing up to him.
7. Learn first skill at level 1. This will help you to gather waves
together and will increase melee's wave-clear ability rapidly.
8. Don't use second skill to get into enemy team. It should be
used when being targeted, usually used when Omen already
gets into enemy team and uses his ult successfully.
Passive:
Every time Omen hits an enemy with a normal attack, he gains one Thirst point. After reaching five points, Omen increases his movement speed by 60 and his attack speed by 25% for 5 seconds. His strengthened Normal attack will also deal 60 true damage and reduce the cool-down for Death's Beckon and Untouchable by 1 second.
Omen's third normal attack triggers a second hit that deals 50% damage. The counter is reset after reaching 5 points of Thirst and after coming of Thirst.
Omen passive can reduce his skil cooldown.In other words, Omen can transfer attack speed into CDR.
True damage occupies Omen damage about 1/3. He does not need armor pierce, unless facing a very tanky team.
Best backline protection in a teamfight is a smart Omen!
Flicker is essential. Flicker + ult = wrecked squishy. And save your Untouchable when the enemy is going to use a burst skill, like Valhein or Murad's ultimates.
Ability Combo: Death’s Embrace(Ult) + Untouchable(B) + Death’s Beckon(A)