Here are some ideas, changes will be in bold.
Shuckle
Item-Leftovers
Evs-252 Def, 252 Sp Def, 4 Hp
Nature-Careful
Ability-Contrary
Moves-Toxic, Power split, Rest, Shell Smash
This is fine, I wont change anything here.
Salamence
item-Salamenceite
Evs- 252 Sp. Attack, 252 Speed, 4 HP
Nature- Modest
Ability- Intimidate--> Aerilate
Moves- Draco Meteor, Hyper Voice, Hydro Pump, Flamethower
You have more physical attackers, go with fully special Mence, EVs to maximize damage, use this variety of moves for coverage.
Ferrothorn
Item-Rocky Helmet
Evs-252 Def, 252 Sp Def, 4 Hp
Nature-Sassy
Ability-Iron Barbs
Moves-Leech Seed, Toxic, Power Whip, Protect
A true stalling set, takes away opponents HP with leech seed and toxic as yours goes up through leech seed. Use Protect in order to gain HP back. If you want Stealth Rock, or a damaging move could replace toxic. Power Whip so your not taunt bait.
Magnezone
Item- Choice Specs
Evs-252 Sp Att, 126 Def, 126 Sp Def, 4 Hp
Nature- Modest
Ability-Analytic
Moves-Thunderbolt, HP Fire, Flash Cannon, Volt Switch
Can really hurt their team with the choice specs, HP Fire is used for coverage, and modest for the extra power.
Tyranitar
Item- Life Orb
Evs- 252 Att, 252 Speed, 4 HP
Nature- Adamant
Ability-Sand Stream
Moves-Earthquake, Dragon Dance, Stone Edge, Crunch
Use Dragon Dance to set up, with life orb, he will be doing massive amounts of damage. Stone Edge and Crunch are STAB, Earthquake is nice coverage.
Arcanine
Item- Assault Vest
Evs-252 Att, 252 Speed, 4 Hp
Nature-Naive
Ability-Intimidate
Moves-Extreme Speed, Wild Charge, Overheat, Close Combat
The assault vest gives him very nice bulk, and more than covers the drop from his Naive nature. Overheat is STAB and since it is his only Special Attack, the stat drop does not cripple him, then proceed to use his nice physical moves. Wild charge was used over Outrage so he does not become confused.
So I hope you liked what I had to suggest, and have a great summer!
-Unstoppable