Step-by-Step Mission Guide (by Soilofgenesis)
1)    Finish the Prologue at the Entrance (remember to bring Assassin Shiki for bond)
2)    Finish 101, farm 10 Zombies in 101 to unlock 102.
3)    Finish 102 and 104 to unlock 201
4)    Farm 20 Ghosts in 201 to unlock 103
5)    Farm 20 Skeletons in 103 to unlock 202
6)    Farm 20 Puppets in 202 to unlock 203
7)    Finish 203 to unlock 204, then complete 204,302 and 303
8)    Farm 10 Female servants in 203 to unlock 301
9)    Farm 30 Fujino Ghosts in 301 to unlock 304
10)    Finish 304 to unlock 401, then complete 401,402 and 403
11)    Farm 15 Assassins in 403 to unlock 404
12)    Finish 404 to unlock 501, then complete 501 and 502
13)    Farm 200 Ghosts in 502 to unlock 504
14)    Finish 504 to unlock 603 (Assassin Shiki permanently joins your roster)
15)    Finish 30 missions and complete Forest(hint: use the saber shiki support to instakill the giant ghosts), use the 2 knives you got to ascend Assassin Shiki twice.
16)    Farm 200 Skeletons in 603 to unlock 503
17)    Clear up any missions you missed until you finished 60 missions (refer to chart for best suited nodes)
18)    Farm 20 Fujinos in the Parking Lot to unlock 604
19)    Finish 601,602 and 604 to unlock 703.
20)    Farm 200 puppets in 602 to unlock 701
21)    Finish 701,703 and 704 to unlock 801
22)    Farm 200 Fujino Ghosts in Parking Lot
23)    Farm 200 Zombies in 802 (if 802 is too hard, do 101) to unlock 702
24)    Finish 702 to unlock 803
25)    Finish 801,803,804, all rooms completed
26)    Finish remaining missions, wait for the last 2 missions to unlock. Farm Parking Lot for Lanterns/Clear Shop in the meantime.
27)    Finish the rooftop. Event complete. Clear shop/Farm Lanterns in Parking Lot for rest of event.