According to Official Guinness Records,
The fastest marathon by a mascot (female) is 3 hr 58 min 57 sec and was achieved by Rachel Bown (UK), running as Mr Hippo from the Brain Tumour Support charity, at the 2016 Virgin Money London Marathon, in London, UK, on 24 April 2016.This was Rachel's 14th marathon. As an ambassador to the Brain Tumour Support charity, Rachel wanted to run as their mascot and achieve the record to raise awareness for them.
For a complete list of 2016 records, please visit 2016 Guinness Records in United Kingdom.