Welcome to the end!
This one’s a bit trickier to get, not super obvious. Here’s what you need:
1.) All pirate tokens (All bonus levels unlocked, you can check by seeing if they’re all in the netherworld.)
2.) 150 points (two ways to check this, but one involves already having this achievement. Quit to the title screen and then check how many points you have out of 350.)
Beat all levels in the main game. This will send you to the netherworld, where you can play through the additional levels there and any unlocked bonus levels. If you’ve already exited, you can reenter through the portal right outside the pirat e’s bay.
Enter into the gate area, should be the middle of the branch. Head right in front of the gates and make a downwards attack. If you meet the point/token requirements, the gates should open. Repeat for all three gates.
You should have unlocked a level at the very very top of the branch, complete it and the achievement should pop. WARNING: This is unlike almost every other level (most like VHS), and it is VERY DIFFICULT. Good luck…