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
You can find a Light Ball in Pokémon Mystery Dungeon: Explorers of Darkness by exploring certain dungeons like Mt. Travail, Surrounded Sea, or Miracle Sea. Light Ball is a rare item that occasionally drops from defeated enemies or can be found in item spawn points throughout these dungeons.
There are 19 floors in Mt. Travail~Ninjachoco~(19)
Mt. Travail 1F - 19F Very Rare
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.
Drowzee is at the top of the Mt Travail dungeon.
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)