Rushing with ninja
Sprites: You can’t really take that much damage from anything but the sprite gods so just hold that space key and go!!
UDL: With a decent amount of def and a 70/70 pet, you can do basically the same thing as you do in sprites. Without, you may want to be a bit more careful. Rush past basic rooms but slow down and kill the monsters that give the slow and quiet effect. Always stop before slime rooms and evaluate whether you can rush through and stay alive or whether you should slowly clear.
Sew: KILL EVERYTHING IN YOUR WAY. If you ever drop below 60ish % health, just back off and try to heal up a bit. Remember ninja, (unless you got a bunch of def), can only take a limited amount of hits. I would personally recommend a t12 katana for killing because most other katanas are limited by the size of the room.
Abyss: Abyss is a scary place for ninjas. Even though I have a incredibly powerful pet and I had a incredibly powerful ninja, I sometimes had troubles rushing abysses on ninja. If you really want to rush, you may want to first get a kageboshi (for the extra defence) and some form of ring that offers def (ubdef, pyra, bracer) Remember when rushing, def likely matters more then hp. Then, hold that space key and hit whatever is in view. Use a high dps katana such as sullen blade or t12-13 and remember to maneuveur around lava.
OT: Dodge. Never get below 50% health, and never, unless you’re actually good at dodging, try to rush past those seahorses. Once more, keep a t12 katana so you can quickly destroy crowds before crowds destroy you. Don’t worry about speed so much because you’re char matters more then a cbow or ctrap(or you shouldn’t really be rushing anyway)
Tomb: Keep a high tiered katana. Don’t get paralyzed, always be speedy and don’t stop moving.
Nest/Halls: Don’t