Well... I've got some progress with my idea so I decided to make a post here
Some secret base specialized in alien studies captured a UFO with alive specimen. Short time later an accident happened at this base (maybe aliens decided to rescue their comrades and sabotaged the base..?)
One of alien containments was broken and the gray prisoner was able to escape. To get out the base he has to roll as a ball very quickly and find an exit.
Some level sketches