I don't know why I put that extra jumping spot at the beginning of the dungeon.
At least that switch by the other gap creates the convenient short cut.
The mini-boss is based on tiles from FF XII: Revenant Wings and is called Atlas.
The boss is in the database with the same descrption and sprites.
You're right about that one Skulltula being on the same time period as the trading spot.
It becomes available after completing that trade and returning.
Speaking of which, taking notes or screenshots of the various locations you're suppose to go is definitely advised.
There's a Nayru encounter you've already had that you might want to return to, outside level 8.