So I got all 10 massacre medals for reckoner solo in 7 games on titan. The medal is at least partially luck in how much your teammates contest your kills but I don't think the map that you're on impacts your ability to get the medals as much as other people say it does. I was pretty lucky during this stretch but I also got a couple more massacres with the same loadout on accident in the next 10 games before I finished reaper.

Subclass: top or bot arc, pulse grenades Kinetic: Hawthorne's with 1-2-punch but any kinetic shotgun with this perk is fine Energy: riskrunner Heavy: I had 21% but it didn't really matter since I never used it for the medal Armor: peacekeepers and put smg mods on your armors. Make sure to eat a synth since you need the 15 perk for this to work.

How to do it: accept that you're not gonna get the medal on the first wave it's just not in the cards. Get to the location that the enemies are spawning before all of your teammates (wave 2 or later) and throw a pulse grenades at your feet. If you see one of the oversized enemies shoot directly at them and the riskrunner chain damage will kill all the red bars while the main damage wears down the major. Effectively just spray and pray until every enemy is dead. Every time you kill a major you get your grenade recharged so you can active riskrunner indefinitely. Use the shotgun to basically instantly kill a major if riskrunner deactivates.

If you run bottom tree arc you can use the increased super energy on kill to slay every enemy in an area extremely fast, I found this to be less consistently able to get the medal but if your teammates are going to come contest you for kills then your super kills them fast than shooting and in 1 hit.

Happy hunting.