Reaper excels at taking out targets in close range. He's particularly effective against tanks. His pick rates in high ranks are quite low but he has his niche uses.
Strong burst damage at close range
Can one-shot and two-shot most of the heroes in this game, given you are close enough to them and aim for the head/neck area
Gets out-ranged quite easily against other damage dealers, specifically Hanzo, Pharah, and Widowmaker
Has very limited mobility compared to other offense heroes
Has to reload quite often due to his shotguns only having eight total shots per reload
Reaper is, by and large, a tankbuster since he has the second highest DPS in the game behind Bastion. He can also burn through most barriers within seconds, or he can enforce the backline, preventing your healers from dying early by denying diving tanks like Winston from reaching them.
Choose Reaper when you need a lot of damage in close ranges. Good situations include when the enemy composition runs aggressive tanks like D.Va, Winston, and he gets a lot of ultimate charge from killing Roadhog.
Wraith Form gives Reaper invulnerability and the ability to move through players for 3 seconds. His movement speed during that time is 7.1 meters per second. Note that he can use health packs and receive healing while in Wraith Form, but cannot take or receive damage. Use it as a disengage tool, not as an engagement option.
Shadow Step allows Reaper to teleport to any flat surface that players can stand on within 35 meters. It only makes a sound to the enemies if you are very close to them. Use it to set up sneaky ultimate usage.
The Reaping is a passive ability that gives Reaper 20% of the damage he deals back as health. Note that the only damage that gives him back health is to enemy players’ health pools (not shields, barriers, turrets, etc.).
Reaper’s ultimate, Death Blossom, is an AOE ultimate. It deals 170 DPS within an 8 meter radius with a movement speed of 3 meters per second.
There are a few ways to play reaper, and which one you should do is mostly based on personal preference and team comp. The one that a lot of new reaper players use is just the plain flanking style. This is where you simply get behind the enemy team, and start shooting them. This strategy works at lower levels of play, but falls apart once people learn to focus you down and listen for your teleport. The second is the “pouncing” style, for lack of a better word. The way you play it is to wait, usually on high ground, for somebody on the enemy team to be vulnerable. Once they are, you jump down and focus them with your powerful potential two-shot kill. This method is similar to the plain flanking method, but is more effective at higher ranks because you teleport to a place they can’t hit you. They also cannot hear you falling, so it’s more surprising to the enemy team. The main problem with this is that you have to wait a lot, meaning you have to get good at timing when you should jump down. You also must not do what a lot of new players do and start focusing a new person because they’re closer and easier to hit. The third and final playstyle is where you play him like a bodyguard. This is where you stick with your team, and play with them, unlike the other two play styles. Reaper is great at deterring flankers, making him great at being a bodyguard for supports. This also allows you to more successfully fight against characters you have good matchups against that try to dive your backline. The main problem with this strategy doesn’t come as much from the other team, but instead from your team. If your team is mostly mid to long range heroes, you won’t be able to get close enough to the enemy to unleash your devestating DPS.
Reaper works well with all of the healers. Lucio’s Speed Aura Amped Up gives Reaper the ability to move as much as he wants during his ultimate, which allows for easy kills. Ana’s Nano Boost helps by either giving him ultimate faster, or making him practically unkillable during his ultimate. He would deal 255 DPS (Damage Per Second) during his ultimate if he is Nano Boosted. Zenyatta’s Orbs of Discord allow for Reaper to kill enemies faster or from farther distances, due to the 30% damage increase to the discorded target. Mercy is a strong pocket healer, and has damage boost, which can make Reaper quite devastating to face in duels. Reaper synergizes well with Reinhardt and Zarya. Reinhardt’s ultimate, Earthshatter, can stun enemies long enough for Reaper to kill them with Death Blossom. Zarya’s Ultimate, Graviton Surge, pulls enemies to a small black hole. This allows Reaper to use Death Blossom and get a wipe on all of the heroes that are not tanks, and the tanks can get cleaned up soon after. Zarya can also bubble Reaper during Death Blossom, which gives Zarya charge and prevents crowd control effects from affecting Reaper during Death Blossom. Reaper can do some serious damage when Mei’s Blizzard is active; it freezes enemies in place so that you can either Death Blossom all of them, or shoot particular targets to get ultimate charge for the next push. Reaper works best when a longer range hitscan hero is played alongside him, whether that be McCree, Soldier, Bastion, or Widowmaker.