Klinklang has one trick up it's sleeve that make it viable in RU: Shift Gear. Shift Gear raises both speed and attack making Klinklang a potent late game cleaner in just one turn. With Klinklang's relatively good bulk and coveted Steel typing it is able to set up a Shift Gear without much trouble against walls like Golbat and Aromatisse. After a Shift Gear boost Klinklang will be able to outspeed to entire unscarfed metagame and even quite a few Choice Scarf users like Braviary. After a Shift Gear boost it also hits quite hard with it's other signature move Gear Grind which can even go through Substitute's. Klinklang also becomes difficult to revenge kill after a boost thanks to it's good base defenses allowing it to tank some priority hits. Lastly there is also Klinklang's ability Clear Body. While Clear Body doesn't come in handy all the time it can help against Intimidate users like Hitmontop and it ignores Sticky Web's speed drop which can really help against Sticky Web teams.
However Klinklang is not without it's fair share of flaws. Outside of Shift Gear and Gear Grind Klinklang's movepool is extremely shallow. Return and Wild Charge are the only physical coverage moves Klinklang gets which leaves Klinklang walled pretty easily. Cobalion, Doublade, Magneton and Gligar are all common Pokemon that can wall Klinklang without too much trouble. Due to this Klinklang will need quite a bit of support in removing these Pokemon. However even with the support it needs Klinklang still holds a solid niche in the RU tier.
name: Shift Gear
move 1: Shift Gear
move 2: Gear Grind
move 3: Return / Wild Charge
move 4: Substitute / Wild Charge
ability: Clear Body
item: Leftovers / Life Orb
evs: 80 HP / 252 Atk / 176 Spe
Shift Gear, Klinklang's signature move is first on this set. Shift Gear is the main move here as it allows Klinklang to raise both his speed and attack in one turn making it a good late game cleaner. Gear Grind is the second move on this set as it is the only physical STAB move Klinklang gets. With an effective base 100 power and the ability to break Substitute's it is a great move and should be used on any Klinklang set just like Shift Gear. Return gives Klinklang the best neutral coverage alongside Gear Grind so it's the preferred option. Return also has a generally high base power of base 102 and doesn't have any drawbacks to using it. Substitute is the last move on this set. Substitute acts as a safety shield for Klinklang granting it the ability to bypass status as well as making him more difficult to revenge kill. With Substitute Klinklang can set up on the likes of Cresselia, Jellicent and Alomomola without fearing any status which makes Substitute the preferred move in the last moveslot. Wild Charge can also be used on the last two moveslots instead of Return or Substitute. Wild Charge give Klinklang the ability the hit specific targets like Moltres and Slowking harder while also being Klinklang's best move against Steel types. However due to the fact that it doesn't give much additional coverage alongside Gear Grind and it's annoying recoil makes it an inferior option most of the time.
The EV spread listed allows Klinklang to outspeed up to max speed Adamant Braviary before the Shift Gear boost. Max attack is used to maximize damage output since and the remainder of the EVs is put into HP for extra bulk. However if you don't feel the need to outrun those Pokemon you can run a bulkier EV spread of 252 HP / 252 Att / 4 SpD. Since Klinklang can outspeed most of the RU tier at +2 without speed investment this spread can also be a good option. For items there is the choice between Leftovers and Life Orb. Leftovers should be used in conjunction with Substitute as it gives Klinklang more longevity and allows Klinklang to set up multiple Substitute's without losing too much HP. However if you are not running Substitute then Life Orb is the main choice. Life Orb trades in longevity for the ability to hit much harder. Both are good options and the item choice mostly depends on the moves of choice. Clear Body is the only ability that Klinklang should use. Clear Body prevents Intimidate from working and ignores Sticky Web's speed drop. Not like Plus and Minus have use in single battles anyway.
Klinklang is a Pokemon that is best used late game. Once all it's checks and counters are gone only then will Klinklang be able to sweep. Setting up a Shift Gear with Klinklang isn't really all that difficult thanks to his good amount of resistances and above average defensive stats. Walls like Aromatisse and Golbat are perfect set up opportunities for Klinklang since it can take any hit from them and set up a Shift Gear. If you are running Substitute then Klinklang can even set up on Pokemon like Cresselia and Alomomola without fearing possible status. Walls often have trouble breaking Klinklang's Substitute while Klinklang's moves do pretty good damage to them at +1.
Hazards are fantastic support for Klinklang as they help wearing down most of it's counters. Spikes in particular helps as it is more useful for wearing down Steel types, Klinklang's greatest enemy. Good users of Spikes include Accelgor, Qwilfish, Roselia and Omastar who can all help Klinklang ensure a sweep. Since Steel types give Klinklang trouble Pokemon that can effectively get rid of them are also great team support. Dugtrio can effectively trap all of the Steel types in the tier bar Bronzong making it a fantastic teammate for Klinklang. Fire types like Emboar and Moltres can take on most Steel types of the tier with ease making them great team options. Slowking and Jellicent can defeat Cobalion one on one with either Fire Blast or Scald for the former or burning with Will-O-Wisp for the latter also making them solid team options.
Klinklang's movepool is barren so you won't find many options here., however there are a few things Klinklang can do that haven't been mentioned. Klinklang has a decent special movepool consisting of moves like Flash Cannon, Thunderbolt, Volt Switch and Signal Beam. however the fact that Klinklang's special attack is only average at best and lack of boosting moves makes it a poor option. Certain types of Hidden Power can be used to lure in specific targets. Hidden Power Fire lures in Steel types and Tangrowth while Hidden Power Ice can lure Tangrowth and Gligar, however these moves have little use outside of the specific targets. Magnet Rise can be used for predicted Earthquake's and let's you be able to set up on Gligar and Rhyperior. Lastly you can use a resttalk set with Shift Gear and Gear Grind but since Steel isn't a very good attacking type it makes it a rather poor option.
Checks & Counters
**Steel types**: Steel types are the bane of Klingklang's existance, with their high defenses and resistance to Gear Grind and Return they can easily take any hit Klinklang throws at them. Steelix stands out as the best counter to Klinklang as it resists Gear Grind and Return, is immune to Wild Charge and can either Roar away boosts or do heavy damage with Earthquake.
**Physical walls**: Pokemon with high defensive stats like Gligar and Tangrowth can take on Klinklang well thanks to their high defenses.
**Emboar and Moltres**: Both Emboar and Moltres can take a hit from Klinklang without much trouble and hit back hard with their STAB Fire moves. Moltres has to be wary or Wild Charge though.
**Bulky water types**: Bulky Water types like Jellicent and Gastrodon resist Gear Grind and can take a Return without much trouble. However most of them bar Gastrodon, Lanturn and Seismitoed have to watch out of Wild Charge.