Go to Archer's Pass, but first, complete Chapter 2 to teach Fidget the Lightning Spell, and get the Ugly Pendant (should be in a treasure chest in the caverns if I'm not mistaken).
Now get to the first vertical right turn on the map (you'll see huge statues in the background), gather as many enemies as you can, stand in the corner and use B then Y repeadtly to power-up Lightning Storm after Lightning Storm, I climbed up to a 3000-something combo in a few seconds. Don't forget to run away before an enemy hits you and breaks your chain, or remove the pendant and re-equip all your highest power-ups to clean up the remaining foes.
If your stamina turns low or you turn red because of the Dust Storm, try to land a few hits with X to cool down, there's bound to be a blob in the group of foes, so if it gets too close between the electric shocks, try to counter him and hit him a bit to get some breathing space, however if you're around level 18/19 on Normal you should have little to no trouble. On Tough or Hardcore you might want to level up your Health, Defense and Fidget a tad more to play it safe, also stock up on food.
The trick here is that the Ugly Pendant divides your Attack, Defense and Fidget power by 10. So, if you remove all of your power-ups to keep your base attack, the pendant will only let you use a 10th of that (I have a base attack of 58 since I put some level gems in it, I only had 5 after equipping the pendant).
The video (not mine, btw.)will show you where to stand to get maximum efficiency, it suggests you spammed the Dust Storm, which can be a good strategy, but the Lightning Storm cranks up the hit count much faster.
Also, since you already leveled up quite a bit, you'll have some good gear as well to finish the job.
EDIT: Corrected the chapter number, and added a few clarifications and corrected typos.