Non-puzzle solution: You'll get this in the middle of level 6-1, Mustacho's Dungeon.
Puzzle solution:
*** Spoiler - click to reveal ***Fall through the hole in front of you and go left. Make a branch, transfer the fire to the branch, and break the door on the right. The stairs in the next room are a trap, so jump off the slide at the bottom and use the lever. This room has a button to stand on to call an elevator. Take out the Bomber above, then beasts will come from the right, left, right, two from the left. This is a good alternate area to get Deadshot.
If you don't stand on the button, you can get an evil eye through the right door when they've stopped spawning. Stand on the button to call the elevator, then run onto it. The elevator will drop you into a large room. Make a branch to the left in the top right, create a vine that attaches to it, then climb the vine to get on the top floor. Transfer the fire to either branch and that should get the guards' attention so you can kill them. There's evil eyes and amulet pieces here, but the option to continue is the middle left. Transfer the fire to the top branch, then attach a vine and sever the branch so you can fire from the middle of the room.
Draw the vine to continue up, and in the next room, create a branch to make a bridge, then draw a vine at max length to attach to it. Climb down the branch onto the vine, then destroy the branch. Once you land on the grate at the bottom, the achievement is unlocked.