I'm going to assume this is for OU.
Lucario
Lucario is too slow and doesn't match up very well against some notable defensive Pokemon like Landorus-T. If you want a Fighting type, Urshifu-R is faster, has immediate power, and doesn't lose to Landorus-T and other bulky Ground types. If you want a Steel type, your best choices are Ferrothorn and Heatran, Ferrothorn for its useful Spikes support and defensive utility with Iron Barbs and its wonderful typing and movepool.
Urshifu-Rapid-Strike @ Choice Band
Ability: Unseen Fist
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Surging Strikes
- Close Combat
- U-turn
- Aqua Jet
Ferrothorn @ Leftovers
Ability: Iron Barbs
EVs: 252 HP / 4 Def / 252 SpD
Sassy / Careful Nature
- Spikes
- Leech Seed
- Knock Off / Body Press
- Power Whip
Dragonite
Dragonite should be using Heavy-Duty Boots to not make Multiscale completely useless and to protect against stealth rock in general. Dragon Claw is pretty bad so you should get rid of it with Dual Wingbeat, a STAB move that is actually good. Roost should be used over Extreme Speed since you already have Dragon Dance making this less useful, and Dragonite really wants recovery to abuse Multiscale as much as possible. Earthquake is preferred over Fire Punch for the ability to hit Heatran and Tyranitar, among others. However, while Dragonite is viable, you're going to want a Defogger, and Corviknight is the best choice for this.
Corviknight @ Leftovers
Ability: Pressure
EVs: 252 HP / 168 Def / 88 SpD
Impish Nature
- Body Press / Brave Bird
- U-turn
- Roost
- Defog
Mimikyu
Mimikyu is also not good. Too slow to pull off a sweep, Shadow Sneak is not enough, cannot switch into anything, outclassed as a ghost type attacker by quite a lot of things and as a fairy type attacker by stuff like Clefable. Dragapult is both fast and powerful and forms an excellent core with either Urshifu-R and Ferrothorn, either wearing down Tapu Fini and beating each other's checks or abusing Spikes with its powerful attacks and U-turn and having a defensive backbone if it needs to switch out.
Dragapult @ Choice Specs
Ability: Infiltrator
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Shadow Ball
- Draco Meteor
- U-turn
- Hydro Pump / Flamethrower / Hex
Zeraora
Zeraora isn't doing too well right now. Tapu Koko is a better Pokemon right now due to its ability to actually damage Landorus-T, its stronger Electric attacks, and unblockable momentum move in U-turn. With Roost it can soft check threatening Pokemon like Tornadus-T which Zeraora can't do because of its mediocre defenses and lack of recovery.
Tapu Koko @ Heavy-Duty Boots
Ability: Electric Surge
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Thunderbolt
- Dazzling Gleam
- U-turn
- Roost
Sylveon
Sylveon is bad and your team wants a Stealth Rocker. Landorus-T is probably the best Pokemon for the job. Stealth Rock + Swords Dance Garchomp should be run on Ferrothorn teams.
Landorus-Therian @ Leftovers / Rocky Helmet
Ability: Intimidate
EVs: 252 HP / 164 Def / 92 Spe
Impish Nature
- Stealth Rock
- Earthquake
- U-turn
- Knock Off
Gastrodon
Tapu Fini is a better choice on a non-Ferrothorn team, as it can handle Urshifu-R. In that case, you can get rid of Corviknight for a Heatran or something like that, since you can run Defog Tapu Fini. Tapu Fini also notably helps against Weavile and Heatran which are becoming more popular. On a Ferrothorn team you can use Toxapex and keep Corviknight, since it provides useful Toxic Spikes and makes what is probably the most infuriating defensive core in history since lando + blissey.
Tapu Fini @ Leftovers
Ability: Misty Surge
EVs: 252 HP / 64 SpD / 192 Spe
Timid Nature
- Scald
- Moonblast
- Knock Off
- Defog
Toxapex @ Black Sludge / Rocky Helmet
Ability: Regenerator
EVs: 252 HP / 144 Def / 112 SpD
Bold Nature
- Toxic Spikes
- Scald / Knock Off
- Recover
- Haze
Pokepaste 1
Pokepaste 2
Don't have time for descriptions or anything like that
