If you see Reaper coming, Its already way to late.
How to Play Reaper
Reaper is the most lethal up close hero. Move him from one target to the next quickly. Best used on enemies with low health or have become separated from their group. Type of hero that can get up close and personal before dishing out pain. Reaper can also take 50 point of health from every kill, making him a true reaper. This is how to play reaper.
Hellfire Shotguns – These are his core weapons and they can dish out a ton of damage. But there is alot of spray in their use, hence shotgun in the name. Therefore you got to get close. They can still do some damage from range but getting close it the key here
Wraith Form – When in Wraith Form, Reaper will be immune to all damage but incapable of firing his own weapons. you do move quicker when in this form which makes this useful when trying to escape and get to safety or when trying to get back to the battle quick after re spawning. Using Wrath Form removes and debuffs on Reaper as well.
Shadow Step – Most powerful ability. Allows you to mark a point within your field of view and immediately jump to that part of the map. Use this to pick about enemies defenses. Shadow step + Hellfire Shotguns = PAIN.
Death Blossom – Ultimate Ability. When used, Reaper’s weapons fire rapidly at all nearby enemies. Yet he can still be taken down when using the ability.
Pharah – This Hero avoids Reaper’s greatest strength (flanking), but keeping up high and raining hell down from above.
McCree – Reaper and McCree assume similar roles in Overwatch, but Reaper’s ability to use Wraith Form and escape McCree’s stun grenade gives him the overall edge in this duel.
Lucio – Lucio’s heal-over-time and speed buff effects both make like very difficult for a Reaper on patrol. His Ultimate ability also directly counters Reaper’s.