Slip Saddle is a very steep and sustained 3.5 km, grade 6 downhill ride. In places the trail is rutted and sometimes rocky but mostly the turf is tussock covered. This is a very demanding trail but if you crash out there is a good chance you'll survive in most places. As downhills go, it's up there with the best.
It starts about a third of the way up Coro XC. You have to watch out for it - it heads off behind you as you come out of a switchback. There is no sign.
At the bottom you have to take the Bush Creek track to Arrowtown. Hence you really need a shuttle to take you up to Coronet Peak and to pick you up at Arrowtown.
You might as well do the Coro DH trail while you're up there and make an afternoon of it. The Coro DH starts at the top of the Coro XC trail. It's rockier at the top and steep but mellows out as it goes down.