OFF BY 1 ERROR
you have an off by 1 error, either the last zombie never shows or the level is complete before the last zombie is killed. this is an off by 1 error, but its not consistent. the first time i played the wave was complete before the final zombie. after the boss killed me on wave 15 i restarted the game and there was 3 bullets and 2 blood spatters STUCK on the screen distracting the hell out of me, but i continued. i got to level 15 and YET again an off by 1 error, this time, the last zombie did not show, take this down and fix it because i've seen other people have said the same thing, fix and i'll give you 10/10