Saints Row

Doc Ketchum's Murder Circus is a rogue-lite mode based on the Boot Hill mission from the main game. For each run, which take around 10-15 minutes each, you have to complete four survival challenges where you or the enemies have a random buff on each one. You can also find 3-4 chests around that grant you additional weapons. In each run you'll get Boot Coins, which can be used between runs for making upgrades to your characters and additional weapons and perks for the chests. There are four characters, each with a different starting weapon, special ability and perk.

To unlock the Murder Circus Finale, you must reach the maximum level of 8 with a character. You gain XP from getting kills and completing the survival waves. I'd recommend saving 5,000 coins before buying anything so you can buy the Prodigy upgrade that increases your XP gain on all characters. Depending on if you have this it can take 3-5 runs to reach level 8.

Other than the XP Boost, i'd recommend using your coins on the blue skills as they are persistent across runs and don't require you to get them randomly out of the chest. The game is pretty easy anyway and the default weapons and the ones already available from the chest are good enough to get you by. One tip is to use takedowns whenever you can to heal yourself. The bonus objectives (x headshots, double kills, etc) are not required but are recommended where possible as they grant extra XP and coins.

The next time you start a run with a level 8 character, it'll start as normal but the final survival challenge will contain a miniboss which is more like a damage sponge alongside a bunch of other enemies. Complete this wave to complete the finale and earn this trophy.