Okay, since noone used my previous suggestion, why not do it myself?
Heatran @ Leftovers | Flash Fire
Timid | 4 HP / 252 SpA / 252 Spe
- Substitute
- Roar
- Fire Blast
- Earth Power
This set is very, very similar to the one already proposed, but with one key difference: it doesn't need to rely on Fire Blast (8 PP and bad accuracy) or on WoW (even worse accuracy) to beat Kyurem. It can switch in on anything except Dragon Tail safely (and even if it switches into DTail, it doesn't do much anyway). Then, once in, you can set up Substitute no matter what, since +0 DTail cannot break it, and +1 DTail has a small chance to do so (and it would imply that Cube didn't Sub on the switch, which is potentially unsafe if we go for a strong Fighting poke afterwards). Then just Roar. The result is a Heatran with a Substitute intact and a Kyurem-B forced to take SR damage once more, possibly Spikes, and that needs to find another free switch / free turn to set up Sub or to Roost / boost its damage. And, even in the unlikely event of a +6 Cube (or just a Cube with a relevant number of boosts), Heatran can solve everything coming in and just Roaring after something dies, since it won't take any damage (and even if it takes a +6 DTail for some reasons, it deals 70% max anyway).
This Heatran has huge synergy with hazards setters, since things like Ferrothorn, Forretress and Skarmory can lure Fire attacks / attackers that are generally countered by Heatran's typing and ability, and it can take full advantage of hazards by shuffling (even its own counters thanks to Sub) with Roar.