According to Official Guinness Records,
The fastest half marathon by a mascot is 1 hr 37 min 3 sec and was achieved by Kenny Steele (UK) during the Inverness Half Marathon in Inverness, UK, on 8 March 2015. Steele was dressed as Bobby the Bee, the mascot for Highland Hospice.
For a complete list of 2015 records, please visit 2015 Guinness Records in United Kingdom.