My first thought was simply taking damage any time you let an enemy pass, like in a tower defense or something. But I get wanting to keep the game clean. It's a fantastic result for the timeframe and the experimental idea.
Which was also something I threw around in my head! But opted to not use it just to keep it tight - one hit and you’re dead.
Y’know, in hindsight I think that had movement been a 2-character command instead of 4 or 5 players would instinctively move more just by virtue of how easy it would have been. Thanks for the kind words though, appreciate it.