Manx Cat patronus ... I had the same type of wand as Ron Weasley's first wand (Ash, Unicorn core), the one that backfired terribly on him (e.g. the eat slug curse against Malfoy) until it got broken by the wamping willow. It was a hand me down from his brother Charlie (The dragon guy), doomed to fail on him from the start as this type of wand can't be passed down [worse with a unicorn core].