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Commander Keen Episode 6: Aliens Ate My Babysitter! (or simply Keen 6) was developed by iD Software and published by FormGen. It is a stand-alone episode, having both a demo version containing a portion of levels and a paid version with all of them. Having bested the Shakadi in the "Goodbye, Galaxy!" games, Keen is stuck home one day when he learns that his babysitter, Molly McMire, has been kidnapped by the giant bird-like species of Bloogs: he travels to Fribbulus Xax, homeworld of the Bloogs, in order to find Molly and prevent her from becoming supper. Though this is definitely a challenging game played normally, this Galaxy games features a unique bug that gives Keen the opportunity to finish levels in record time, completing all ten required levels in less than four minutes.

== Overview ==

In order to win the game, Keen must find (and collide with) Molly, triggering the end-game sequence. Molly is found in the Bloog Control Center, and there are a number of gateway levels and required items to be used on that map in order to reach that level. Specifically:

* The grappling hook and rope found in the First Dome of Darkness is used to cross a chasm
* The "Stupendous Sandwich of Chungella IV" found in Bloogfoods, Inc. is used to feed a giant creature that otherwise forbids passage
* The Bloogstar Rocket Passcard found in Bloogton Tower is used to ride a rocket

Including Bloog Control Center, there are ten levels in all. There is no known way to break the map itself to approach the end-game faster: therefore, the primary objective is to find ways to either complete levels as fast as possible, or reach the necessary item in the level as fast as possible. Thanks to the bullet collision bug in this game, however, Keen can exploit a number of other glitches that achieve this much faster than simply making his way through each level.

=== Categories ===

This game is run using version 1.0. This version allows for extra glitches and provides better performance for a number of wall-clips. If necessary, there are ways to downgrade a legit copy of the game from 1.4: you can find patches for that [http://dosclassics.com/keen/dl.php?id=of here].

The '''any%''' run is played on Easy difficulty. Due to the glitches used, fewer enemies and more shots per ammo pickup makes the run as fast as can be.

The '''glitchless%''' run is defined as using no unintended skips caused by various glitches. This includes all of the Impossible Bullet Trick variants, gem storage, death-exiting, and any map clipping errors. Currently, the run has been routed for Hard difficulty, which is marginally faster than Normal difficulty: Easy may be faster than either, but Hard showcases a lot of special movement and challenge that would be otherwise omitted.



== Glitches ==
[[File:Keen6 glitch bullet collision.gif|framed|right||Bullet Collision Glitch]]

This section addresses game-specific glitches only. For glitches spanning the entire Galaxy set of games, check the [[Commander Keen: Galaxy#Glitches|Galaxy engine page]]. Similarly, are glitches specific to a level are addressed in the appropriate section.

=== Gem Storage ===

Any gems (colored keys) picked up but not used in a level are kept by Keen until they are either eventually used or Keen dies. This also includes collecting a gem and restarting the game (a very important point if you're attempting glitchless runs!!). Only one gem of each type can be stored in this way.

=== Bullet Collision Bug ===

Bullets are considered solid at the very top of their sprite: this includes both Keen's own bullets and laser bullets that emit from gun hazards. The cause of this is unknown, but may be related to the collision used in this game's switches or by the Gik enemy.



== Impossible Bullet Trick ==

In many ways, the Impossible Bullet Trick (hereafter referred to by its abbreviation, IBT) isn't a single glitch but, rather, a collection of glitches. It is also usable in a variety of ways, and therefore it warrants a separate section dedicated to explaining the practical applications in detail.

=== Setup ===

At its core, the IBT is typically a combination of two glitches:

* Bullet Collision Bug, found only in this game
* [[Commander Keen: Galaxy#Platform Teleporting|Platform Teleporting]], occurring in any Galaxy game

To make use of this glitch, use the following procedure:

# Jump straight up in the air
# Shoot down about two-thirds to Keen's terminal velocity
# If #2's timing is correct, Keen will land on top of the bullet for a brief instant:
## For a vast majority of uses, the bullet will be timed such that it hits the ground just as Keen lands on the bullet. This produces the IBT most are familiar with, and is used with rocket jumps and stepladders.
## Rarely, the bullet will instead be jumped upon before it collides with terrain. This is the IBT setup required for double jumps.

Technically, this can also work while Keen is moving sideways, but the perceived timing (and correct line-up of where Keen needs to be) can make this more challenging to do.

The timing of the IBT is much easier to realize on Easy difficulty than on Normal or Hard, thanks to the former's lesser gravity, though it is important to note that it also takes longer to set it up for the reason. Optimization of IBTs requires that the player jump as low as possible, further increasing the challenge of timing.

=== Execution Types ===

There are three variants to IBT. Each has its own uses and all should be learned and understood.

{| class="wikitable"|style="background: none;"
| The '''rocket jump''' is the most common usage of the IBT, and also the most spectacular to behold. After setting up on the ground, shoot up to perform the rocket jump: this teleports Keen to the bullet he just shot, traveling at a high speed upwards for as far as the bullet can go. This is the IBT used to exit levels quickly, in combination with other glitches. || [[File:Keen6_IBT_rocket_jump.gif|frameless|center|Rocket Jump IBT]]
|-
|The '''stepladder''' is a smaller trick but is useful as a setup for rocket jump IBTs. Set up on the ground next to a wall, then shoot at the wall: this causes a shot to fire and immediately explode, and the explosion lasts long enough to act as a platform that Keen is then teleported to. || [[File:Keen6_IBT_stepladder.gif|frameless|center|Stepladder IBT]]
|-
|The '''double jump''' is by far the most difficult IBT to perform, requiring a very different setup in its practical applications. While high in the air and timing the bullet, hold the jump button (with or without pogo, depending on what's needed) to have Keen jump on the bullet. For vertical distance this is useless, as the rocket jump is faster, but the double jump can allow Keen to traverse large horizontal gaps. The setup for a horizontally-moving double jump is as follows:

# Use an IPT to jump as high and as far as you can 
# As Keen reaches the highest part of the jump, halt Keen's horizontal motion
# Shoot downwards with the same timing as before
# Prepare the pogo and/or hold jump
# Immediately as Keen begins to jump, begin moving Keen horizontally again
# If needed, repeat steps 2-5 until Keen arrives at his destination

As implied above, it is possible to chain double jumps together. This is never required in any of the speedruns and is exceedingly difficult to pull off anyway.
|| [[File:Keen6_IBT_double_jump.gif|frameless|center|Double Jump IBT]]
|}

=== Applications ===

The Impossible Pogo Trick, by itself, gives Keen the capacity to cross large vertical (and sometimes horizontal) distances far faster than normal. The most prominent example of this is the First Dome of Darkness, in which the grappling hook and rope are picked up without the use of activating an elevator. It is also necessary to skip most of the Bloogton Tower.

However, there are plenty of instances where simply moving fast is not enough. None of the Guard Post levels need to be crossed vertically, only horizontally, and often involving gem-door fetch quests. To break these levels, we look to the [[Commander Keen: Galaxy#Clipping Through Walls|wall clip]] and [[Commander Keen: Galaxy#Exiting Out of Bounds|out of bounds]] glitches. An example of the process is given below:

# Upon entering Guard Post One, hug the right edge of the map and perform a rocket jump IBT.
# As Keen is moving up with the bullet, hold down to place Keen in a crouching position.
# Once Keen reaches the top of the map, the bullet squishes Keen into the ceiling.
# Because Keen is moving faster way faster than he should be (in pixels per frame), the game mistakenly puts Keen's hitbox up and into the wall.
# Wall clipping forces Keen to move upwards and to the right until he reaches a non-empty space, which is out of bounds.
# Keen entering out of bounds of the level automatically ends the level.

Many applications of the IBT are performed in this way: using a rocket jump to collide with terrain, clipping through the terrain, and making Keen's way out of bounds. In some cases, the stepladder IBT works to properly set up for a rocket jump clip. All IBTs will be explained in sufficient detail whenever they are used.