While like everyone else I like the ideas of dwarfs and bunnymen My hearth will always be with machines. call me a technophille if you want but a race driven by Machines if perfect for me. However lacking any programming skills I can only ever post ideas and concept art. In my head you start with a sort of mechanic only.
he will quickly gain the ability to make new mechanical people
If you wanted to adapt it to the lore you could easily call them planestriders or something and have them be from an alternate plane. Not sure how lore friendly aliens are, but i suppose alternate planes does hint the multiverse.
But then what Evil was it running from? What terror has been unleashed? If it could crush such an advanced civilization, what hope do we mere simpletons have? Pretty much begs for an epic Titan battle at some point.
Yeah maybe a failed plane travel experiment allowed something bad into the world? This would open up for a new titan and explain the single survivor. The fact it’s a new technology explains why the portal broke. Maybe the robots could be made from the broken portal?
Possibly. Maybe his new tech has to be adapted for the stuff he finds in this world as well. Iron instead of whatever he/she had at home. Maybe for a really powerful/efficient robot he needs rare gems or ore to act as conduits for power. You could go in many directions at this point. Maybe you need some form of power instead of food to keep them going.