Aliens: Alien 2 (Prototype)

A lost masterpiece from SquareSoft that was cancelled right before its release, though a MSX version was officially released. Some of the tricks are performed by using bizarre key combos, to pass through the 'impossible' wall in level 1 you need to hold A and Up to do a somersault. And to enter those narrow tunnels: pressing A repeatedly while holding left or right, making the character to crouch.

The game itself is pretty short, four levels and you're practically done.

00:00 - Start
00:50 - Overworld
03:50 - Laboratory Level 1
06:33 - Level 1 Boss
07:21 - Laboratory Level 2
10:16 - Level 2 Boss
10:50 - Laboratory Level 3
13:43 - Level 3 Boss
14:17 - Underground
16:45 - Final Boss
17:20 - Ending