Chargestone Cave contains a number of interesting pokemon, primarily electric and rock types with a bit of steel thrown in for good measure, all in levels 25-28.  Joltik is the most commonly found here, an Electric/Bug pokemon that evolves into the fast, slightly frail special attacker Galvantula.  Galvantula is fairly strong as long as it’s kept clear of Rock and Fire attacks, particularly since the Bug typing cancels out Electric’s weakness to Ground, and Electric typing returns the favor for Flying.  Galvantula has some movepool issues (no access to high power moves other than Thunder, Hyper Beam and Giga Impact), and one of its potential abilities (Unnerve) is largely worthless, but its very particular weaknesses and interesting options (Energy Ball, Electro Ball, Gastro Acid) and the fact that its preferred ability (Compoundeyes) makes Thunder uncannily accurate without Rain Dance support ensure it is a credit to its team.  Klink can be found here as well, the odd, gear-shaped Steel pokemon providing the equally strange presence of a high-speed physical wall and physical attacker at once.  Its Special Defense isn’t anything to sneeze at either, though its relative lack of good physical attack moves (having only Vice Grip, Gear Grind, and Bind naturally) is a bit crippling on the offensive side.

Ferroseed also lurks in Chargestone Cave, and its evolution Ferrothorn is immensely powerful- to the point that it changed competetive battling severely when it was first introduced.  Ferrothorn has frankly massive defenses, weakness only to Fire and Fighting attacks, and decent, almost outright good, physical attack.  This keeps its terrible speed from being a hindrance (particularly if it uses Gyro Ball) and its access to plenty of perfectly good physical attacks in addition to the suicidal Selfdestruct and Explosion attacks only compounds its potential to stall out enemies with Ingrain (as well as Stealth Rock and Leech Seed if you’ve used breeding to put moves onto it).  Just to make things worse, the thing can be taught to Swords Dance- definitely a potent addition to virtually any team.  Much less expressive but nearly as impressive is the impassive Nosepass, whose evolution, Probopass, is among the most defensively strong pokemon around.  Sadly, Probopass has poor offenses, having to rely on a rather staggering array of tricks up its sleeve for a pokemon with no arms on it at all, afflicting its opponents’ status and stats in all manner of ways.

Boldore can be found here as well, just an evolution of Roggenrolla, but rarest of all (and with a power comparable to its scarcity) is Tynamo.  This little thing, with the help of 39 levels and a Thunderstone, becaomes Eelectross, an Electric pokemon that naturally has the ability Levitate, leaving it with an immunity in place of what would have been its only weakness.  Eelectross’ defenses are passable and its speed is a bit poor, but both of its attack stats are fairly high, and it has access to plenty of attacks (both physical and special) to make use of these offense stats in handing out a drubbing.  While most of the attacks it naturally learns are Electric or Poison, it can learn plenty of alternatively-typed moves that are strong enough to be useful.