Flintlock: The Siege of Dawn

As you defeat enemies in the game, you will see a number in white on the side of the screen. You will also see a yellow % number which will act as a multiplier for the white number. You can manually claim this number at any time by pressing  and it will automatically be claimed any time you are hit by an enemy, fast travel, or rest at a lodestone/camp. The trick to this achievement is both killing many enemies in a row without getting hit as well as building up a multiplier by doing different actions such as full attack combos, perfect dodges, etc.

Now, if you were to go for this achievement legit it would be a bit of a nightmare. Being a soulslite the combat can be tricky and there are often ranged enemies you don't notice that will shoot you and kill your chances. Luckily, there is a handy exploit that will hopefully not be patched out, which you can see in the video below. Once you get to the third map toward the end of the game called "Dawn" you can head to the location in the video with an enemy that continuously spawns two other enemies. The exploit comes into play in that you can mark them with Enki's  attack from a distance, then back up and they eventually despawn and it counts as you killing them. You can attempt to get your % multiplier up before coming here so you can claim the XP prior to the 50k required, or just build up all 50k at once and claim it with no multiplier. Either way, once you bank a full 50k+ at once, you'll get all the reputation achievements. Continue banking XP until you have about 100k so you can then head to camp and begin upgrading all your equipment.