This engine is based on the locomotive now running on the Whipsnade Zoo Railway called Superior.  Building on their experience with Excelsior, Accucraft have built Superior with larger cylinders and a stainless steel superheater.  The loco has internal gas firing and the smokebox door opens to aid lighting. The boiler has a water level check valve with the overflow piped away below the frames and the lubricator is fitted with an underfloor drain tap, both of which help to keep the cab free from excess oil and water.

The loco is dual gauge and is supplied with alternative pony trucks for 32mm and 45mm gauges.