Your go to weapon here are thousand daggers. The reason why is because they cause large amounts of damage and gives you brief invulnerability, which allows you to be grazed by anything. What this means is when you cast the spell card you graze hp and mp and time from nearby projectiles, which is frankly OP. I recommend activating thousand daggers when a bullet storm type of attack happens, like Nitori's purple laser storm or Flandre's rune bullet thingy (I don't know the name) Anyways, you want to stay in time stop at virtually every other time because it allows you to cast thousand daggers and recover your mp/time(through being near projectiles) and because of this combo you can unstop time and stop it again to recover your daggers and cast thousand daggers again. Looping this again and again allows you to deal massive amounts of damage in a short amount of time. I'm not bothering to count, but its likely that I spent more time in time stop then in regular time and that in regular time, the fight probably only took about 1 minute.

• While my example is the Nitori/Flandre fight this can be done at any boss fight after getting thousand knives.
  
• This can be done through chainsaws, but its much harder. To do it through chainsaws it must be a destroyable projectile, and you throuw a chainsaw right before the projectile hits you, which blocks all projectiles after it for some time and if you are near enough it also grazes.
  
• I realize I could do this better, and that I am probably not the first, but this is what I use to deal with bosses and I created a guide first
  
• -from ArtemisHunt "When using thousand knives in Time Stop, the knives that exceed your permitted knives are not counted, so be careful. The only workaround is if you use thousand knives around 41-45 TIME then you'll be able to sidestep this limitation. " basically what he means is that you can only throw as many knives as you have in time stop E.G. if you only can throw 27 knives in time stop you'll only throw 27 knives when casting thousand knives. However, if you start thousand knives in time stop and it doesn't end when your time runs out it continues casting in non-time stop aka real time