Reposting this video from the lucky dodges threadI took the time to test some stuff in this game last night. I think the main thing worth noting is that bosses (and I think midbosses) don't have a collision hitbox (or at least they don't seem to do). I've sort of demonstrated this with ZUN. I've also checked with the TLB and you can safely fly over her (I believe I sort of demonstrated in my full run since I think I was able to safely move over the wings). Also checked this on Letty on easy mode and I find myself getting killed by the bullets she spawn while I try to fly over her body. Pretty useful with Marisa since her focus laser actually seems more powerful when you are at point-blank range. As for dodging patterns, I think I did show some potential use of flying over bosses in the video even if I did mess up a bit.
Also noticed that Marisa probably has the best survival between the three characters if you have the autobombs on(at least in my opinion). I guess its a quirk with her autobomb since while the autobomb does take 3 power away, its not as bad compared to the other characters since hitting a boss with it will make them drop power items (you get about 1 bomb back from what I noticed). Not sure what Sanae's autobomb really does, and Reimu's seems to be a screen clearing bomb that has an explosion that lingers for a few seconds.
The MS spellcard actually has a behavior if for some reason you managed to get out of that pocket of space you are supposed to dodge in. ZUN starts firing a lot of bullets. I actually thought it was just behind him until I tried going to the sides (and in one particular case, circle around him). This is the only case I know where an enemy fires more bullets if you go to a particular spot (haven't really tried on the other bosses yet).
Side note: I think the fairies still have a collision box to worry about. Was ramming into them when I did a test on collision hitboxes in stage 3 on easy. I've also gotten myself killed on the third lifebar of the TLB as it was preparing for its second attack. I believe it was due to the yin-yang orbs hitting me as I was sitting on top of the TLB.