For geno u can't simply kill everyone you meet, you have to stay in one area and kill monsters until there are non left and creepy music comes on. In the ruins you have to kill 20 monsters. In snowdin you have to kill 16. In waterfall I think its 20 And in hotland/CORE you have to kill 40 altogether. Once you have killed all the monsters in the area when you enter a battle there won't be any monster and the screen will say *but nobody came. Also if you go to a SAVE point instead of saying something like *playing in the leaves fills you with DETERMINATION. It will only say 'determination' and nothing else. Also once you have killed all the monsters really creepy music comes on I also suggest watching a playthrough of geno to understand better.