The eight-year-old has always been held in very high regard by the Irish champion trainer and was considered one of the bankers of last year’s Festival when beaten by the ill-fated Brindisi Breeze in the Albert Bartlett Novices’ Hurdle.
He scraped home when a 1-5 favourite on his chasing debut at Navan in December, but showed improvement when getting up right on the line at Leopardstown last month.
Mullins feels a similar level of progress is required, and he is also concerned about the prospect of testing conditions. He said: “I’m hoping that if he improves as much from his last run to this run as he did from his first run over fences to his second, then he’ll have a chance. I think he will have to improve that much to win.
“I’m happy with him, but I would have preferred drier ground.”
Mullins has a second representative in Terminal, who has won his last two races over the larger obstacles.
“He’ll be a bit of an outsider but he’s done nothing wrong, he jumps well and stays, so he deserves his chance,” said the trainer.
Disputing favouritism with Boston Bob is Unioniste, trained by British champion Paul Nicholls and the choice of Ruby Walsh.
The five-year-old won a valuable handicap at Cheltenham in December before just beating fellow RSA hope Hadrian’s Approach in a thriller at Newbury.
Nicholls said: “He won a handicap at Cheltenham and he stayed the trip well there. He jumps well and we ran him plenty short at Newbury – he was going to run at Fontwell as Dynaste was going to Newbury but then he didn’t go.
“He has improved enormously since then, soft ground will help him and he has a good chance. Ruby is very keen on him.”
Nicky Henderson, trainer of Hadrian’s Approach, is hopeful his charge remains very much on the upgrade.
He said: “He made three shocking mistakes up the straight and only got beaten a short head at Newbury. He was closing all the way to the line against Unioniste.
“He’s in good form and has been improving all year. I think he’s really getting the hang of it now.”
After deciding to send long-term RSA favourite Dynaste to Thursday’s Jewson Novices’ Chase, David Pipe relies on Goulanes, who made a winning debut over fences in the Towton Novices’ Chase at Wetherby.
Pipe said: “He will like the ground and will have no trouble staying the trip, he might even want a bit further.
“It could turn into a slog and if it does, that will be in his favour.”
Lord Windermere and Lyreen Legend were both within a length of Boston Bob at Leopardstown last month, giving their connections hope.
Lord Windermere’s trainer Jim Culloty said: “He’s got solid form on pretty heavy ground, but I personally think he’ll be better on better ground.
“He’s a laid-back individual, which I think will help him get the trip.
“He has decent form over two miles so he’s not a slow horse.
“He’ll travel and jump and I think he’ll get himself in a good position two out.
“I’m not sending him over for the good of his health.”
Lyreen Legend is trained by Dessie Hughes, who said: “I’m looking forward to seeing him running. He’ll go on the ground and he’ll get the trip, so we’ll see how he gets on.
“I think our horse is a bit fitter now than he was that day and I’m very happy with him.”