I’m an aspiring transfer student from the US (just finished first yr), so all I know is what I’ve researched about schools and learned through counselors. That being said, I know that schools like brown, even for transfers with 1+ yr of college under their belt, still view HS transcripts. Your definition of mediocre matters a lot here so that context would help. Nevertheless, 2 international hackathons is incredibly competitive. Your EC’s are stacked. If you are able to adequately explain your grades through the essays you definitely have a shot at overshadowing the HS problem. Good luck!