Last year's winner Ziga Boy is among a 16-strong field declared for the Sky Bet Chase at Doncaster on Saturday.The Alan King-trained grey defeated Coologue by three and a quarter lengths to take the prize 12 months ago and the latter, from Charlie Longsdon's stable, is again in opposition. Longsdon also saddles Long Lunch.The weights for the three-mile feature are headed on 11st 12lb by Venetia Williams' Tenor Nivernais, the Colin Tizzard-trained Third Intention and Jonjo O'Neill's Holywell. O'Neill is also responsible for Another Hero.Paul Nicholls is double-handed with Scottish National hero Vicente and Caid Du Berlais.Other trainers with two runners are Rebecca Curtis with Potters Cross and Bigbadjohn, and Nicky Richards, who has Ballyboker Breeze and Looking Well.Completing the line-up are Southfield Royale, Out Sam and Katachenko.