Here are the fastest paths for farming: Thanks to Tsunaka for this guide.
Chapter 1: Run to the right and up to the (not yet flooded) merman room. If you're not Shanoa, jump kick off their heads to get to the ledge. Very straight forward after this.
Chapter 2: a) Proceed normally up till the fire room, use invincibility frames to get to the other side (puppet/heal/martial arts, etc.) Flip the switch and continue normally.
b) Proceed normally to the two switch sliding door area, hit the switch and backslide to open it up without help. Proceed to the open room with the scales, get up to the first ledge on the right by jumping off the skulls if you're not Shanoa. Wait a few seconds and a ghost should be coming along shortly enough to jump kick up to the next floor. Head right to the boss switch and kill away.
Chapter 3: Up, right, down, hit boss, hit knee while walking left, get on ledge of your choice, shoot at heart/face/knee as you please. Not many shortcuts to speak of... Could probably imp jump (let an imp follow you and use it to jump kick off) so you don't have to go all the way around.
Chapter 4: a) Go through frankenstein up to dullahan, up to bubble doggies, up to imp. Take imp back down to the right of dullahan area and imp jump up to the painting. Jump down and imp jump up the moving platform area. Done! Soma can imp jump off Yorick's Skull by using it on the ledge under the painting and jump kicking forward immediately; puppet master is helpful if you don't get the timing perfect.
b) Proceed to the imp, and immediately imp jump up to the chest above you, head left to the switch and proceed as you please.
Chapter 5: Head up the clock tower and out the top left. Climb down, to the ledge with 3 skele gunners and wait for death's scythes or imp jump if you dragged one along (harpies work too.) Anyways, imp jump off your imp/scythe/harpy up Shanoa's magnet, head left and up to the boss. Be sure to thank Death if you used his scythes. He's so helpful.
Chapter 6: Too straight forward =[ Use whatever you can to get past Final Guards, take damage so you get knocked past them. This chapter is packed full of food so that's not a real worry.