These are so cool! Feels a bit like Christmas here this morning!
What actually happens in the game is that the lander (green and yellow), picks up the humanoid and carries it to the top of the screen with it dangling beneath it.
This opens up the opportunity for you to shoot the lander, but not the humanoid.
Then the humanoid falls away and you must rescue it by catching it.
If a lander gets to the top of the screen it slowly sucks it up into itself and then changes into the mutant. Which as you noticed is kind of a lander with a humanoid merged with it.
So that last shot would be quite good as the mutant. They're meant to be pretty fugly.. So cutaway like that is probably more authentic... We'll maybe jazz it up a bit with some particle effects in the homage too... I am sure The Vid Kid (Eugene Jarvis) would appreciate that.. He likes particle effects!