According to Official Guinness Records,
The fastest marathon dressed as a witch (female) is 3 hrs 26 min 13 sec, achieved by Nicola Nuttall (UK) at the 2017 Virgin Money London Marathon, in London, UK, on 23 April 2017.This was Nicola's second year running the London Marathon as a witch.
For a complete list of 2017 records, please visit 2017 Guinness Records in United Kingdom.