2-1 (The Coast)

Map

2-1 is the Pickup Clip gauntlet.
The main progression of the level is to the right, so we can pickup clip to bypass every single GBA section in the level.
Most skips in this level are 2-tile clips, other than the house screen, which is just 1-tile.

Gem Routing

There are two screens with tons of enemies, meaning we can benefit a lot from keeping combos intact.

Start with the three 100 gems on the house screen (from cutting the bush, under the rock, and killing Shadow Link).
Collect everything from combos and gem rain on the crabs screen.
Ideally you want around 1000 minimum entering the purple octoroks screen (can be less if you're confident with your combo). If you need more beforehand, you can grab the 100 gem from the cave.
On the second big bomb screen, you can get about 360 gems between the 100 gem in the chest and the sunken 20s (plus a little extra in 5s).
The Lobster will drop 500+.