Kolakoski

Score: 71.25 (pass)

#!perl -l
$_.=($x=$ARGV[$i%2])x(/./g,$x)[$i++]while$i<500;print substr$_,0,pop

Score: 74.24 (pass)

#!perl -l
$_.=($x=$ARGV[$i%2])x((/./g)[$i++]||$x)while$i<500;print substr$_,0,pop

Score: 79.25 (pass)

No comment.

#!perl -l
$_.=($x=$ARGV[$t])x substr$_.$x,$i++,1,$t^=1while$i<500;print substr$_,0,pop

Score: 81.25 (pass)

Dang substr and ARGV! I hate them! Hate them, I say!

#!perl -l
$_.=$ARGV[$t]x substr$_.$ARGV[$t],$i++,1,$t^=1while$i<500;print substr$_,0,pop

Score: 83.24 (pass)

Fourth try. Dang substrs. I need to get rid of them.

#!perl -l
$_.=($x=$ARGV[$x==$ARGV[0]])x substr$_.$x,$i++,1while$i<500;print substr$_,0,pop

Score: 101.23 (pass)

Third try.

#!perl -l
@c=($a,$b,$M)=@ARGV;{$x=$c[$x==$a];$_.=$x x(substr($_,$i++,1)||$x);$M>length&&redo}/.{$M}/,print$&

Score: 131.28 (pass)

Second try.

#!perl -l
($a,$b,$M)=@ARGV;$_=$a x$a.$b x($a-1?$a:$b);$x=$a;$i=2;{$_.=$x x substr$_,$i++,1;$x=$x==$a?$b:$a;$M>length&&redo}/.{$M}/,print$&

Score: 172.28 (pass)

First try.

#!perl
($a,$b,$c)=@ARGV;$_=$a x$a;$i=1;$x=$b;if($a==1){$_.=$b x$b;$i=2;$x=$a}while(length $_<$c){$n=substr($_,$i,1);$_.=$x x$n;$x=($x==$a?$b:$a);++$i;}$_=substr($_,0,$c).$/;print;