The escapee from Sokoban

After escaping from Sokoban, our main character gets attacked by zombies. Fortunately, they find a submachine gun with infinite bullets. 

How long can they survive?

Controls:

Mouse only. Move your mouse around to move/aim towards a spot.

When you die, your score is revealed.

What is this?

This game was made for #TweetTweetJam 3, the goal was to make a game with code that fits in 2 tweets (560 characters.) Here is the GMS2 code below (run this in the draw event of an object that you place at the topleft corner of the game):

if x==0 {f=99 t=f s=0 g=f*f u=f v=10 repeat f {y+=1 i[y]=-9 j[y]=-9 k[y]=0 l[y]=1 h=0 n=0 o[y]=g p[y]=g}}
c=mouse_x-u-4 d=mouse_y-v-8 h=h>f?0:h+1 y=sqrt(c*c+d*d) i[h]=u j[h]=v k[h]=9*c/y l[h]=9*d/y
u+=s<1?sign(c):0
t+=1 if t>f {t=0 x+=1 repeat x {n=n>f?0:n+1 o[n]=random(999) p[n]=144}}
y=0 repeat f {y+=1 i[y]+=k[y] j[y]+=l[y] draw_text(i[y],j[y],".") o[y]+=o[y]>u?-2:2 p[y]+=p[y]>v?-2:2 if abs(o[y]-u)<9 && abs(p[y]-v)<9 {s=x f=0} draw_text(o[y],p[y],"Z") z=0 repeat f {z+=1 if abs(i[y]-o[z])<9 && abs(j[y]-p[z])<9 {i[y]=g o[z]=g}}}
draw_text(u,v,s<1?"@":s)