Playing through mercenaries to unlock handcannon. The Waterworld flashing black screen bug really made playing it almost unbearable. It's also really tense with Leon having a Super Salvador running at you and the screen goes black. Alot of aim at head and pray you hit while the screen is black.
I have 5 stared all the stages with Leon and now I'm going through with Ada. I hate having to redo the stages again to unlock the handcannon, but it's a necessary tedium I guess. Once I unlock the handcannon, I can just play mercenaries for fun and goof off for long kill chains.
A word of advice though for the castle, I'm not sure if the Castle level is bugged for everyone else, but the enemies will effectively stop spawning once you go up to the balcony area. You will need to have a large kill chain in the initial starting area for as long as possible before you head upstairs through the door, if you want to 5 star.