V2.

This level consists of 'layers', areas with their own themes, tileset, music and boss(es), each with their own sets of enemies and challenges.


Most mandatory layers have four quadrants:

- The NW quadrant is where you enter the layer from.

- The SW quadrant leads back to the Lift, a column of screens which can take you up to any previous layer, or to The Surface, an area with infinite health, infinite weapon energy and a shop.

- The NE quadrant leads to the boss of that layer. You need all the boss keys of the four main layers (layers that are 2 screens tall) to finish the level, as the final boss is locked behind those keys. (These keys are blue.)

- The SE quadrant leads to the next layer.


Purple keys are obtained by completing the challenge within the purple portal on every layer (except the Surface). These keys are used to access the Lift in the SW quadrant of all layers except the first main layer and the lowest layer, which are free to enter.
Purple keys can also be used in the shop on the Surface to unlock Pile Driver and Magnet Missile, weapons that can open weapon energy caches in some layers or dig through the floor in other layers, skipping a major part of the layer below.


Notes:

- If you don't want to complete the NE quadrant of the ice layer, you can reach the boss room from the end of the SE quadrant. You won't be able to access the nearby checkpoint, though.

- There are four secret bosses throughout the level, hidden within the orange portals in some of the layers. They give orange keys, apart from the last boss' red key. (The first secret boss is on the Surface: go right, past the shop...)
-- You can use all the secret boss keys to unlock the final boss, instead of the regular blue keys. The main difference between this secret route and the normal route is the bosses you face and the weapons you unlock, but both paths have a healing weapon, a miniboss shredder, a spammable weapon and a chargeable weapon.

- After defeating the final boss and getting the weapon required to access the Energy Element in the shop, you unlock the full version of the Lift, which goes down as well as up. There are also boss refights there with gimmicks brought back from different parts of the level, to spice up each battle.