Here's a few things I was thinking that might make a realistic take on this trope:
They wouldn't size-shift.
They wouldn't breathe in space(Unless they have enough dna of a creature that can survive without a spacesuit, such as tardigrades[ www.dailymail.co.uk/sciencetech/article-1054351/Tiny-w...tml ])
They wouldn't use magical powers.
They wouldn't be even part demon
They also have a chance of borrowing elements of a Real Robot( https://en.wikipedia.org/wiki/Real_Robot link