What can I do to drop a data file mistakenly created and currently with 0 byte and in offline (needs recovery) state?
You can not drop the datafile. You can move it to a better location and keep it there. If you want to get rid if it, re-create the tablespace and copy the data to the new tablespace. Drop the old tablespace and rename the new tablespace. Don't forget to give quota to your schemas similar as they have on the old tablespace.