I liked the concept, collecting -> assembling -> defense flows pretty well.
I think execution of defense part has some flaws though. It seems impossible to fully block those attacks, so 3/3/3 fire/ice/missile is nessesary. I tried 4 missile and 1 ice at first try, and dying at defense part from ice attack didn't feel really fair.
But that aside, it had its own charms like graphics and final twist in the story. Nice job :)