Synonyms for Befoul:

n.

besmear, bespatter, spatter, attack, smut, denigrate. befoul (noun)
foul, maculate, defile.

v.

change (verb)
foul, maculate, defile.
contaminate (verb)
dirty, defile, pollute, stain, soil.
dirty (verb)
defile, smudge, dirty, besmirch, foul, smear, putrefy, taint, sully, streak, tarnish, pollute, soil, smirch, stain, contaminate, muddy.

Other synonyms:

besoil, smutch, begrime, denigrate. besmear. smut, bespatter. spatter, blacken. black. blacken
smudge, begrime.
darken
blacken.
Other relevant words:
bespatter, blacken, begrime, denigrate, maculate, besoil, smut, besmear, spatter, smutch, black.