Magcargo is usually relegated to NU due to its many shortcomings as a defensive Pokemon, mostly courtesy of its typing. Weaknesses to Stealth Rock and extremely common attacking types such as Water and Ground, an underwhelming set of resistances, and a rather paltry HP stat mean the poor snail doesn't see daylight too often. However, with good all-around defensive stats, a surprisingly good support movepool, and an alternative Rock-typing that serves it well when countering some of the most prominent threats in the UU metagame, Magcargo finds itself in an interesting niche.
Magcargo is often overlooked in UU due to its low stats and weaknesses to common attacking types, but it can still fill a respectable niche as a wall. Despite Magcargo's lowly reputation, its respectable 50/120/80 defensive stats allow it to serve as an effective counter for some powerful sweepers. Magcargo's Fire/Rock typing, despite giving it 4x weaknesses to Water- and Ground-type attacks, is very useful, giving it resistances to Flying-, Poison-, and Normal-type attacks while reinforcing its Fire-type resistance. Combined with a usable Special Attack stat and a serviceable support movepool, Magcargo can be a useful niche counter to certain threats while supporting his team.
Magcargo is a great switch-in against Normal-types without effective coverage moves, such as Ambipom and Swellow, or those that are Choice-locked into a Normal-type move, such as Choice Band Kangaskhan or Tauros. Magcargo can also comfortably take on and force out dangerous Fire-type sweepers such as Arcanine and Moltres. Lava Plume is the STAB Fire-type attack of choice thanks to its high burn rate, which has the potential to give a Rhyperior or Azumarill switch-in a nasty surprise. Flamethrower may be used in that slot, but Lava Plume is generally preferred since Magcargo is not trying to overpower its counters, so a little extra power does not make a large difference. Hidden Power Rock is Magcargo's strongest option for a secondary STAB move, hitting Fire-types for solid damage. Recover gives Magcargo reliable recovery and allows it to stay healthy through repeated attacks and residual damage. There are a multitude of options for the last slot. Stealth Rock is always useful for residual damage, while Toxic and Will-O-Wisp can be used to spread potentially crippling status ailments among the opposing team. Toxic is great for hitting bulky Water-types looking to switch in for free, such as Milotic, Blastoise, and Slowbro, while Will-O-Wisp cripples physical attackers such as Rhyperior and Feraligatr.Team Options & Additional Comments >>>
Magcargo doesn't have a slew of viable move options outside of those that have been mentioned on its main set. Earth Power attains super effective coverage against Rock- and Poison-types; however, Magcargo must rely on hitting its opponents as they switch in, as most of those Pokemon can outspeed and OHKO it. Explosion can be used if you're willing to go out with a real boom, but won't be doing much more than trashing Magcargo's defensive potential, given its unimpressive Attack.
Due to Magcargo's access to Light Screen and Reflect, as well as Memento, a dual screens support set is a possibility; Uxie's able to do that better, however, with fewer exploitable weaknesses and superior Speed. Magcargo also has access to an interesting setup move in Curse, and thus the option of employing a boosting set under sandstorm. Nevertheless, given the high number of weaknesses it bears to common attacking types, this set is usually better left for Pokemon like Cradily. Finally, employing a Choice Specs set is a possibility if you desire to deal some real damage with Magcargo, but other Fire-types such as Magmortar and Moltres tend to do that better with their higher Special Attack stats and superior movepools.
Even though Dugtrio is by no means omnipresent, it is the ultimate hindrance to all sorts of defensive sets Magcargo could ever dream of running, thus making Shed Shell a viable option over Leftovers.
Checks and Counters
Just about anything that has decent Special Defense, isn't weak to one of Magcargo's STABs, and bears a move that hits it for super effective damage can be considered a counter. However, every Pokemon that relies on physical attacks to beat it must be careful not to be burned by either Will-O-Wisp, Lava Plume, or Magcargo's Flame Body Ability. Water-types that carry Rest, such as Milotic and Lanturn, are prime examples of counters, being able to switch in on all of Magcargo's attacks with ease, including Specs Hidden Power Grass, and retaliate with Surf. Omastar can make use of its 4x resistance to Fire and decent special bulk to scare Magcargo away and set up multiple entry hazards. However, it won't enjoy being hit by Toxic, Earth Power, or Hidden Power Grass. Claydol, with its naturally high defensive stats, can switch in with ease and proceed to either spin away the Stealth Rock that Magcargo might have set up or hit it hard with Ground-type moves. In addition to that, because Claydol mostly runs special attacks, it can afford the risk of being burned. Clefable literally walls Magcargo for an eternity and can use the opportunity to Calm Mind up, set up Stealth Rock, or just slowly stall it out with Toxic and Softboiled. While Dugtrio risks being burned by Will-O-Wisp or Lava Plume if it directly switches in, it can trap Magcargo and OHKO it with Earthquake.