This guide is a compilation of information and techniques that are useful to know about.
Videos for glitches and optimal boss fights etc: https://www.youtube.com/playlist?list=PLKcAVgPu-flu1Z6FycLHjPY1J21v8cnmw
Movement The fastest movement technique is dash-cancelling. It's just dashing then cancelling the end animation with a buffered melee attack, so you can dash again quicker than normal. I personally dash, then hold LMB and just time my dashes afterwards. Though you do need to keep your Ki meter in mind, so it's not empty when you need to fight.
Stats The combat/magic value in character panel represent how much extra damage you will do. For example, a value of 10 translates to 1 damage. For comparison, the most damaging sword in terms of combat attack, The Lawgiver, only does 10 more damage on normal hit than the starting sword Nekrom.
Death Touch increases the Combat/Magic stat by 10 each, which means 1 damage, when in Thanatos mode.
Tips When you're low on Ki, make sure to use Thanatos until it builds back up, as your attacks don't consume Ki when in this buffed state.
Miscellaneous Using Lock-On for the Red Lady fights in the Mansion helps when she teleports, as the camera will automaticaly follow her. This makes it much easier that having to look around where she is.
As with the previous game, if you have ~200 FPS or more, the mouse sensitivity might feel be too low even on the fastest settings. But this can be solved by limiting the frame rate of the game to 144 or so.