My favorite is a very general feature - the light-hearted way perl has with context. It is an annoyance to lovers of formalism that every perl builtin and function is free to return whatever it likes for the context it finds itself in. That is the essence of perl dwimmerie.

After you master the difference between list and scalar context, you get to enjoy string and numeric contexts for your values. You can savor the numification and stringification of undef.

Not only that, you get wantarray and use overload for '""', '0+' and 'bool', so you can play the game yourself!

Delicious!