Alright, it took me a while to figure this out, but if you aim right between the eyes with a shotty, then you can get some decently consistent one hits.
Pro tips - you can farm stealing from seedlings for revives. Looks like the final boss is going to be a piece of cake when I get an absurd amount of revives near the beginning of the game.
"Hey, that lava lamp was fine."
"How do you know?"
"It had 3 blues."
"Who are you to say what is right? Since I am the only (and most senior) tester, I am the leading authority. And I think all of them are bad. "
"Bu-"
"Shh..."
Step by step guide of getting 5,000 points in hardcore : 1. Equip melee 2. Hit enemy 3. Spam the F key directly after you hit them 4. Repeat (Don't be afraid to do some normal killing.)
"If you keep on playing you'll keep unlocking things and ultimately get better at the game. Remember to take occasional breaks and do some non-BTD5 things." Okay, BTD4 time!
 "Achievement Unlocked 3"){kind=icon}
 "Road of the Dead 2"){kind=icon}
 "Crystal Story II"){kind=icon}
 "Manufactoria"){kind=icon}
 "Armed with Wings 3"){kind=icon}
 "Elona Shooter"){kind=icon}
 "Thing-Thing Arena 3"){kind=icon}
 "Bloons TD 5"){kind=icon}
 "Idle Mine"){kind=icon}
 "The Last Door - Chapter 2: Memories"){kind=icon}
 "PRIOR"){kind=icon}