Moves
Thanks to Parental Bond, Power-Up Punch hits twice, letting Mega Kangaskhan double her Attack with just one use. Double-Edge is Mega Kangaskhan's hard-hitting STAB move, giving her great offensive presence before a boost and serious wallbreaking power after a boost. However, if you are worried about Mega Kangaskhan getting worn down by the recoil, you can opt to use Return at the cost of making Mega Kangaskhan more reliant on boosting. Sucker Punch gives Mega Kangaskhan a useful priority attack, allowing her to pick off weakened faster threats and even potentially sweep through battle-worn teams. Just note that Sucker Punch can result in mind games due to its failure against Pokemon using support moves.
Earthquake is the most reliable option for the last moveslot, allowing Mega Kangaskhan to slam Steel- and Rock-types and avoid recoil from Garchomp, Ferrothorn, and Rocky Helmet users. Rock Slide doesn't offer great coverage compared to Earthquake, but in exchange, it lets Mega Kangaskhan hit Gengar and Ground-immune Rocky Helmet users such as Zapdos and Cresselia. With the help of Parental Bond, Rock Slide also has a 51% chance to cause the foe to flinch! Finally, Substitute can be used with a bulkier EV spread to allow Mega Kangaskhan to muscle through some of her defensive checks. Even against offensive Pokemon, Substitute can make Mega Kangaskhan extremely difficult to check, as playing around Sucker Punch becomes more difficult. Secret Power offers no additional coverage and is rather weak, but its 51% chance of paralysis and ability to avoid Rocky Helmet damage can make it a good move to pair with Double-Edge.
Set Details
Jolly is the preferred nature for sweeping, as it allows Mega Kangaskhan to outspeed threats such as Landorus-T and Hydreigon as well as Lucario and Kangaskhan before they have Mega Evolved. However, Adamant allows Mega Kangaskhan to be a bigger threat early in the game, as she is thus less reliant on boosting. Maximum Attack and Speed EVs are preferred for maximum sweeping power, while the 4 Special Defense EVs ensure that Porygon2 will not get a Special Attack boost.
Scrappy is the preferred base ability for Kangaskhan. This allows her to hit Ghost-types before Mega Evolving. This is especially important against Gengar, which is a common switch-in to Mega Kangaskhan. Scrappy also allows Kangaskhan to use Power-Up Punch on Aegislash switch-ins, letting her OHKO Aegislash with a +1 Earthquake after Mega Evolving.
If using Substitute, consider a bulkier EV spread of 132 HP / 252 Atk / 4 Def / 4 SpD / 116 Spe with an Adamant nature. This allows Mega Kangaskhan to survive some impressive attacks, such as Choice Specs Latios's Draco Meteor, +2 Aegislash's Flash Cannon, Landorus-T's Superpower, and Choice Band Garchomp's Outrage. The Speed EVs are designed to let Mega Kangaskhan outspeed Breloom. Thanks to the HP EVs, Mega Kangaskhan also takes less damage from Rocky Helmet, allowing her to take on Cresselia, Suicune, and defensive Rotom-W more easily.
Usage Tips
If using Mega Kangaskhan early-game, try to focus on attacking the foe instead of setting up. This is a particularly effective tactic against offensive teams, because even if Mega Kangaskhan goes down early, the amount of damage she will have dealt can open up holes for teammates to sweep. Setting up early may seem appealing, but most teams will have offensive checks that can cut Mega Kangaskhan's sweep short. If your strategy requires Mega Kangaskhan to last longer, focus on using non-contact moves such as Earthquake and Rock Slide early on, as one of the most common responses to Mega Kangaskhan is to switch in a defensive Rocky Helmet Pokemon. Common Rocky Helmet Pokemon to watch out for include Suicune, Cresselia, Zapdos, Talonflame, Gyarados, Hippowdon, Garchomp, Ferrothorn, and Serperior.
When planning to sweep with Mega Kangaskhan, focus on softening her defensive checks such as Cresselia, Suicune, and Porygon2. Doing this can allow Mega Kangaskhan to smash through them with a boosted Double-Edge or Return, leading to a potential sweep!
Usually, it is better to Mega Evolve Kangaskhan on the first turn, as the Speed boost allows her to outspeed important threats such as Hydreigon and positive-natured Lucario. However, if you are facing Gengar or Aegislash, holding off on Mega Evolution can actually be a good idea. Thanks to Scrappy, Kangaskhan can hit Gengar before she Mega Evolves with Return or Double-Edge, making it a less reliable check. As for Aegislash, using Power-Up Punch as it switches in can allow Kangaskhan to OHKO it with Earthquake after Mega Evolution!
During Team Preview, if you notice that your opponent's team is packed with defensive Mega Kangaskhan checks such as Porygon2, Cresselia, and Suicune or contains offensive checks such as Blaziken and Terrakion, don't be afraid to bench Kangaskhan if you feel like other Pokemon provide a better matchup. Mega Kangaskhan may be extremely dangerous, but even she can't bust through an entire team on her own.
Team Options
Rocky Helmet Pokemon such as Suicune, Cresselia, and Hippowdon are huge problems for Mega Kangaskhan, as their good bulk and the residual damage can stop her from sweeping. Knock Off can get rid of their main source of residual damage, with good users including Blaziken, Conkeldurr, and Azumarill. Tricking Choice items onto them can also cripple them. Rotom-W and Rotom-H are the best Pokemon for this job, while Togekiss can Trick them a Choice Scarf as well. Finally, residual damage from sources such as Stealth Rock can weaken foes enough to put them into Mega Kangaskhan's KO range, which can help in avoiding further chip damage from Rocky Helmet. Garchomp, Hippowdon, and Swampert are particularly good users of Stealth Rock.
While using more than one Mega Evolution may seem like a waste of a teamslot, it can work well in Mega Kangaskhan's case provided that they cover Pokemon that give her issues. Mega Gengar is the perfect example of this, as it has Shadow Tag to trap many of Kangaskhan's defensive checks and counters. Mega Charizard X is also a good choice, as it can set up on Suicune and Ferrothorn.
Finally, one notable strategy is pairing Mega Kangaskhan with Lunar Dance Cresselia or Healing Wish Latias. These moves can bring Mega Kangaskhan back from the brink of being KOed, giving her another chance to sweep!