Mr. Big, the Shetland pony who is always in a good mood, was a gift from Sienna's parents on her third birthday. Sienna learned to ride him at an early age. When she moved to the city with her mother after her parents separated, Mr. Big stayed with her father Yann at the stable. But he recognized Sienna immediately when she moved back to Gut Summerset after some years. He is clever and an expert at opening horsebox doors and finding food wherever he goes. He is very fond of children and is now cared for by Sienna's little half siblings Max and Mia.