I can shorten your 36 non-duplicate-letter attempt by 5 chars with: 
#        1         2         3
#234567890123456789012345678901
grep/^(([@_])(?!.*\2))+$/x,<D>;

[download]
I think this trick might be applicable to your others as well...

Update: I'm still trying to grok your longer ones (re eval in golf... coool) and I'm uncovering some oddities: 

qw(a d d) 
   ad
   add
   dad

qw(a d)
   ad
   add  <= wrong... but 'dad' got correctly skipped... I think
                    add gets through because the 'd's are right
                    next to each other

[download]
Doubled letters (dd, tt, etc) are sneaking through... It looks like $n{'d'} needs to be temporarilly decremented when 'd' matches in the character class...

-Blake

In reply to Re: andye Re: "Countdown" (golf) by blakem
in thread "Countdown" (golf) by stuffy

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