Your mistake in this sub:

sub Char{ 
  my $char=400;
  my $hp= $char - int(rand(20)); 
  print $hp ; 
}
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is that you re-initialise the character's hit points to 400 every time you call it. The first line sets their hit points to 400, and then the next line subtracts a random number from it. Why do you need this in a function at all? Isn't it easier to just do

$hp= $hp-int(rand(20));
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instead of calling a function?