I like the concept of creating your own enemy before fighting it but it is a bit rough.
I built a full purple robot with box gloves and it was not there when I fight it, just the plain grey robot. The base idea is good but with more work you can make it really interesting: boss battle drop you new pieces, you gain more points on more difficult pieces and each character has an animation (or at least like the first pokemon games, just attack animation) it will help a lot new players.