Seems like a Battle Spot team to me, as there are 2 Mega Evolutions on the team.
Mawile's pre-Mega ability should be Intimidate to weaken physical attackers before it Mega Evolves.
Anyway, Slowking does heavy specially defensive investment much better than (Mega) Slowbro can, so it should stick to a Bold nature:
-Calm Mind
-Scald
-Psyshock/Iron Defense
-Slack Off
Nature: Bold
EVs: 252 HP/80 Def/176 SDef
Item: Slowbronite
Ability: Regenerator
or
-Scald
-Psyshock/Fire Blast/Ice Beam/Foul Play
-Thunder Wave/Toxic
-Slack Off
Nature: Bold
EVs: 252 HP/232 Def/24 SDef
Item: Leftovers/Rocky Helmet
Ability: Regenerator
or
-Scald
-Psychic/Fire Blast
-Ice Beam/Grass Knot/Psychic
-Slack Off
Nature: Modest
EVs: 252 HP/40 Def/216 SAtk
Item: Slowbronite
Ability: Regenerator
Sludge Wave > Sludge Bomb on Nidoking, so that it won't get walled by Bulletproof Chesnaught. Fire Blast already damages it heavily, but having your STAB move being able to hit it is much better.
Ursaring doesn't need Seed Bomb, as Close Combat already heavily damages Rock (and Steel) Pokemon. It also doesn't need both Earthquake and Close Combat at once, since both offer redundant coverage together:
-Facade
-Close Combat
-Crunch
-Swords Dance/Protect
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Toxic Orb (Jolly)/Flame Orb (Adamant)
Ability: Quick Feet (Jolly)/Guts (Adamant)