Part 1 - 41 chars

sub f{
#2345678901234567890123456789012345678901
(my$i=shift)=~y/_/./;grep/^$i$/i,@{$_[0]}
}
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Part 1 with xtra credit - 55 chars

sub f{
#234567890123456789012345678901234567890123456789012345
my$a=shift;(my$b=$a)=~s/_/[^$a]/gi;grep/^$b$/i,@{$_[0]}
}
[download]

Part 2 may follow later, but I have to get back to work :(