WIGGLER:

About:
Wiggler is a Deepest Sword secret achievment.

Description:
Bypass the last section with the length 4 sword.

How to get:
When you get the Lengh 4 Sword, make it to the 4th level of the cavern, then go as forward as you can (without climbing on anything) and there is gonna be a wall. (how can i say this) Stay as close as you can to the wall and then press M2 (right click). Your sword is going to attach on the top of the wall then try to wiggle around untill you reach it.

GETTING... OVER IT:

About:
Getting... Over It is a Deepest Sword secret achievment.

Description:
Take the upper path with the length 2 sword.

How to get:
When you have the Lenght 2 Sword, go in the first cavern and try climbing on the upper part of the cavern.

HEAD OVER HEELS:

About:
Head Over Heels is a Deepest Sword secret achievment.

Description:
Find a way to stand on Long the Dragon's head.

How to get:
When you have any sword thats Lenght 3 or more try to climb on the dragons head starting from the dragon's nose.

I hope that i've helped you! :)