Suicide Lead Landorus-T doesn't make sense for this team, change it to a defensive set that looks more like this:
Landorus-Therian @ Leftovers
Ability: Intimidate
EVs: 252 HP / 164 Def / 92 Spe
Impish Nature
- Stealth Rock
- Earthquake
- U-turn
- Toxic
This also frees up a slot on Heatran so you can use Toxic to cripple the defensive Pokemon that Heatran traps. You can also try using a specially defensive EV spread with 120 speed and Leftovers to outspeed neutral-natured Magnezone and (albeit less common) Aegislash, since you no longer need it as a rocker.
U-turn is pretty vital to Corviknight, so I would replace Brave Bird because Body Press lets you more effectively hit the likes of Weavile and Bisharp, and you already have a good check to grasses in Heatran.
If you want, you can try using Rocky Helmet on Toxapex to really annoy opposing Urshifus, but this is more of a toss up.
