How many characters of code did you use?
558

If you're comfortable with it, paste your game code here, so we can marvel at your achievement!
k='\u265E'
l='\u2665'
n='\u2716'
y='\u25A1'
d=document
c=e=>d.createElement(e)
b=c('p')
d.body.append(b)
s=b.style
s.display='grid'
s['grid-template-columns']='20px '.repeat(8)
h='innerHTML'
r=b.children
for(i=0;i<64;i++){t=c('i')
t[h]=y
b.append(t)}
z=c('p')
b.append(z)
p=23
m=a=>{v=Math.random()*64|0
return v!=a?v:m(a)}
r[m(p)][h]=n
r[m(p)][h]=l
r[p][h]=k
d.addEventListener('keydown',e=>{
q=e.key
x=q=='a'?p-1:q=='d'?p+1:q=='w'?p-8:q=='s'?p+8:p
r[p][h]=y
if(r[x][h]==l){z[h]+=l
r[m(x)][h]=n
r[m(x)][h]=l}
if(r[x][h]==n)z[h]=z[h].slice(3)
p=x
r[x][h]=k})