no there is not a boss and here is something that might help you Pokemon explorers of time, darkness, and sky all do not have bosses.
on the 20th floor, which is the peak of the mountian.
20 i think
There are 19 floors in Mt. Travail~Ninjachoco~(19)
Mt. Travail 1F - 19F Very Rare
Drowzee is at the top of the Mt Travail dungeon.
After finishing Aegis Cave, wait about 3-5 days, and Bidoof will come looking for you asking you to come to the Guild. Appears that Azurill has a nightmare, and Mt. Travail will be unlocked.
Darkrai will apear in the following places- Mystifying Forest (13F) Crevice Cave (B2F) Miracle Sea (B3F) Mt. Travail (B17F) Spacial Rift (B14F) (with Mystery Part or Secret Slab in the bag)
There are 20 floors in Mt Travail. You can only go with your Partner Pokemon, not your recruited friends.
In Pokémon Mystery Dungeon: Explorer of Time, you can find Scizor in the Mt. Travail dungeon and you can find it on Floors one, two, three, four, five, six through 19 and it will appear randomly throughout any of the floors.
Ok here's the answer 20 floors! geez.
you need mystery part Mystifying forest: B13~Deep Crevice Cave:B2~Miracle sea:B3~Mt. Travail: 17 ~Spacial Rift:B14 hope that helps (VERY hard to recruit, it's a little easier to have a golde mask and then hold it)
Before or after he gets "arrested"? Or after he's released? If it's after he's released, he goes to Mt. Travail (I think that's how it's spelled...I don't have my DS on me right now XD).