Last time I checked, it was 14 floors then you encounter the MASTER OF ALL THINGS BAD. Or, at least on your first visit anyway.
There are 13 floors in the mystifying forest.
14
Mystifying Forest has 14 floors and can be unlocked by defeating Dialga at Temporal Tower. As far as I know there is no DeepMystifying forest.
13 floors then the end
I belive there are aroud 12 floors
13
13 or 14
14, careful...the ''master of all bad things" is on 15!
1 plus boss fight
There are 14 then wigglytuff ang the gulid members (Wigglytuffs HARD!)
Yes you can. You can get them at; bulbasaur(mystifying forest floors 1-13), charmander(dark crater floor 1-10), squirtle(lake afar floors 1-8), pikachu(far amp plains floors 1-4, after graduating from the guild), meowth(happy outlook floor 5-15), chikorita(mystifying forest floors 1-13), cyndaquil(dark crater floors 1-10), totodile(lake afar floor 5-11), treecko comes out to request a job after your battle in the explorer maze), torchic(dark crater floors 1-14), mudkip(lake afar floors 1-9), skitty(happy outlook floors 1-15), turtwig(mystifying forest floors 1-13), chimchar(dark crater floors 1-10), piplup(blizzard island floors 1-10), and munchlax(mystifying forest floors 1-13).
You have to beat the grand master of all bad things in the MYSTIFYING FOREST(14 floors).