Moves
Rock Slide is a reliable STAB attack boosted by Sheer Force. Zen Headbutt hits Fighting-types for super effective damage and is also boosted by Sheer Force. Fire Punch is boosted by Sheer Force and hits the Steel-types that resist Cranidos's STAB move, OHKOing Magnemite and Ferroseed. Superpower has even more power, although the stat penalties often force Cranidos out. It also hits opposing Rock-types hard, OHKOing Onix after Sturdy has been broken. Crunch hits Ghost- and Psychic-types harder than anything else, 2HKOing Slowpoke and Pumpkaboo-XL. If the coverage is not needed, Substitute can be run to give Cranidos a shield from status and to let it dodge Sucker Punch. Cranidos's frailty makes it hard to set up, though.
Set Details
The given EVs maximize Cranidos's Speed and Attack while boosting its Defense by one point. A Jolly nature is best, as it lets Cranidos outrun as much as possible. If Sticky Web support can be provided, an Adamant nature can be used for extra power, but 22 Attack with Sheer Force and Life Orb will usually get the job done. A Life Orb lets Cranidos hit incredibly hard. Sheer Force powers up Rock Slide, Zen Headbutt, Fire Punch, and Crunch, and removes Life Orb's recoil when using those moves.
Usage Tips
This set should not be switched into attacks if possible. Bring it in via a slow U-turn or Volt Switch or after a KO. On standard teams, this set has the role of a wallbreaker, smashing holes in the opponent's team so that something else can clear up later on. On Sticky Web teams, this set can also be used to clean up late-game. Generally, opening with Cranidos's coverage moves is the best idea. The opponent will often switch in their bulky Fighting-type thinking they can force out Cranidos, and Zen Headbutt will usually KO it. If your opponent has no Pokemon left that resist Rock-type moves, spamming Rock Slide will usually get the job done. If you're running Substitute, use it on forced switches and against predicted Sucker Punches.
Team Options
While not vital, Sticky Web support is certainly appreciated to remedy Cranidos's average Speed. Surskit and Sewaddle have the best synergy with Cranidos, as they resist Fighting-, Ground-, and Water-type moves, while Cranidos resists Flying-type moves. As Fighting-types threaten Cranidos, bulky Fighting-resistant Pokemon are a must. Bulky Fairy-types like Snubbull and Spritzee are good teammates, as they can counter Timburr and Mienfoo that lack Poison Jab. They can both also cure Cranidos of status with Heal Bell. Poison-types are also good teammates for the former reason. Croagunk can check opposing Fighting-types and is also immune to Water-type moves thanks to Dry Skin. Wynaut can trap and remove Fighting-types and grant Cranidos free switches with Encore. As this set is walled by Mudbray and Hippopotas, Grass- and Water-types to check them make good teammates. Staryu can hit them both with its Water-type STAB moves and remove entry hazards; Foongus can put something out of commission with Spore as well as wall most Fighting-types; Pumpkaboo-XL can beat both of them with Giga Drain and spread burns with Will-O-Wisp. If Cranidos is on a Sticky Web team, bulky Ghost-types are recommended to both block Rapid Spin and act as Fighting-type switch-ins. Pumpkaboo-XL resists Water- and Ground-type moves and is immune to Fighting, while Cranidos resists Fire- and Flying-type moves. Entry hazard setters like Dwebble and Ferroseed are also appreciated, as the Stealth Rock and Spikes they can set up help Cranidos get additional KOs. Ferroseed resists the Water-type moves Cranidos is weak to, while Cranidos resists the Fire-type moves Ferroseed is weak to.
Other Options
A Rock Polish set using Life Orb or Berry Juice can be a deadly late-game sweeper, but Cranidos's low bulk and susceptibility to priority make it hard to set up and easily revenge killed. Head Smash has incredible power, but its high recoil drastically cuts into Cranidos's already limited durability. Ice Beam lets Cranidos 2HKO Mudray and Hippopotas with Sheer Force and Life Orb, but doesn't accomplish much else that its usual moves don't. A suicide lead set consisting of Stealth Rock, Endeavor, Head Smash, and Superpower can be used, but Onix is usually a superior lead because it has better Speed, better bulk, Taunt, and Explosion. Cranidos does have Mold Breaker, however, so it can OHKO Dwebble and Onix through Sturdy. Lastly, Cranidos can use an Eviolite, but even then it's still not especially bulky and the Speed of a Choice Scarf or the power of a Life Orb is more beneficial.
Checks and Counters
Ground-types Mudbray and Hippopotas can take anything Cranidos has and OHKO with Earthquake. Onix and Diglett using Focus Sash can avoid an OHKO if they have full health, outrun, and OHKO with Earthquake, although Onix is OHKOed by Superpower if Cranidos is running Mold Breaker. While Drilbur can't switch in, it can still outrun and OHKO Cranidos with Earthquake.
Fighting-types Mienfoo outruns Cranidos and OHKOes with High Jump Kick, but a Sheer Force-boosted Zen Headbutt will OHKO if Cranidos is running Life Orb. Timburr can survive the Choice Scarf set's Zen Headbutt and OHKO with Drain Punch, and if Cranidos has taken some prior damage, it can take it down with Mach Punch.
Physically Bulky Pokemon Slowpoke can avoid a 2HKO from a Life Orb-boosted Rock Slide if no entry hazards are up and OHKO Cranidos most of the time with Scald. A Sheer Force-boosted Crunch will always 2HKO, however. Bronzor and Pumpkaboo-XL can beat the Choice Scarf set, but the Life Orb set can 2HKO both with Crunch. Mold Breaker Earthquake can also OHKO Bronzor after Stealth Rock.
Priority Due to Cranidos's frailty, most priority moves can take it down with some prior damage. Timburr, Croagunk, Corphish, and Carvanha all have STAB priority moves that Cranidos is weak to in Mach Punch, Vacuum Wave, and Aqua Jet, respectively.
Faster Pokemon Choice Scarf Mienfoo, Chinchou, and Pawniard outrun Cranidos even in Sticky Web and OHKO with their respective super effective STAB moves, although none of them can switch in. If Cranidos is not running a Choice Scarf, practically any Pokemon with above 16 Speed that can hit Cranidos super effectively can force it out. Mienfoo, Drilbur, Staryu, Chinchou, and Onix are notable examples.