Moves
Boomburst is Mega Rayquaza's strongest move; with the boosts from Aerilate, STAB, and Choice Specs, it is able to 2HKO almost every Pokemon in the game, including Chansey and specially defensive Aegislash, with no drawbacks and the added bonus of hitting through Substitute, making it really hard to switch into and even impossible without a Pokemon that resists Flying or has Soundproof. The next moves aim to patch up these weaknesses, with Techno Blast being able to OHKO physically defensive Soundproof users such as Mega Slowbro and Groudon while still hitting everything else extremely hard and having no drawbacks. Ground coverage is necessary to get past some bulky Rock-types, the main target being RegenVest or Sand Stream Mega Tyranitar, but it is also really useful for Prankster Registeel as well as RegenVest Zekrom and Mega Ampharos that can otherwise switch on Choice Specs Rayquaza and OHKO it back. Secret Sword can be used over Precipice Blades to guarantee an OHKO on Mega Tyranitar, which might be able to recover its health throughout the battle otherwise, especially if it's running Regenerator. In that case, Draco Meteor should be used over Techno Blast, as it still reliably OHKOes common Soundproof users but also hits RegenVest Zekrom and Mega Ampharos. Draco Meteor can also OHKO specially defensive Giratina before it can cripple Rayquaza with status or retaliate with Metal Burst, but the move forces Rayquaza out once used, potentially allowing a Pokemon to set up, and therefore it isn't as easy to use as Techno Blast. Extreme Speed is used so that Rayquaza keeps some of the revenge killing capabilities of standard Aerilate sets, as even without a boost, it hits extremely hard against frailer or weakened Pokemon. It can be replaced with additional coverage, mainly Volt Switch, which allows you to scout the opponent's move as well as weaken potential counters or, in the case of Shedinja, remove them with the support of a Mold Breaker Pursuit trapper. However, Volt Switch does have the negative effect of giving Imposter Chansey momentum. Trick is another option to permanently cripple a wall that Rayquaza might not be able to break or to just ease up prediction in a battle where the boost from Choice Specs isn't needed; it should be used carefully and only as a last resort, as Rayquaza's item is what makes it so threatening, and it becomes significantly easier to handle without it. Finally, Magma Storm can be used as a way to provide Rayquaza with additional coverage and a way to deal with Shedinja. It also prevents foes from switching out, which can help guarantee a 2HKO on Steel-types, but comes at the cost of low accuracy.
Set Details
Maximum Special Attack investment as well as a Special Attack-increasing nature is necessary to allow Rayquaza to properly break common switch-ins. Maximum Attack investment gives Extreme Speed as much power as possible. Aerilate turns Boomburst into a Flying-type move, giving it a staggering 273 Base Power coupled with Choice Specs, which boosts its power just enough to invalidate some of Rayquaza's most common switch-ins. Minimal Special Defense IVs can be used to punish Imposter Chansey harder if it switches into Rayquaza directly but will make Rayquaza a bit easier to revenge kill with special attacks. 56 Attack EVs can be moved to Speed to allow it to outpace 148+ Spe and 252 Spe Kyogre. If no physical move is chosen, Rayquaza can opt for a Modest nature with the Attack EVs moved into either Speed or bulk depending on the needs of the team. Another spread of 4 Atk / 252 SpA / 252 Spe with a Naive nature can be used to outspeed positive-natured base 110 Speed Pokemon such as Mega Latios, Mega Latias, and Mega Diancie, but Rayquaza then has significantly less power and relies much more on entry hazard support and chip damage to get the 2HKOs it needs.
Usage Tips
Boomburst is not only Rayquaza's strongest move but also its safest, as it has no drawbacks, it has high PP, and even if the opponent has a switch-in, they will be forced to recover. For these reasons, it's the move you should be clicking most of the time and start with if you're unsure of the opponent's play. Cases where you wouldn't want to click Boomburst mindlessly are if there's an obvious switch-in like Mega Slowbro on an -ate weak team or Zekrom, in which case aggressive predictions can really put the opponent under pressure from early-game. Additionally, a lot of teams don't have a switch-in to Choice Specs Rayquaza and might want to rely on Shedinja after Choice Specs has been revealed, in which case double switching into a Mold Breaker Pursuit trapper will really put them under pressure. A more defensive team with many pivots doesn't necessarily have to play aggressively, as they can bring Rayquaza in many times throughout the battle. Very rarely switch Rayquaza directly in unless you predict the opponent to switch or recover, as Rayquaza should avoid all kinds of status and most defensive Pokemon in Balanced Hackmons run a pivoting move, making switching in directly often useless. If Rayquaza runs Volt Switch, it's an extremely good way to scout and weaken your opponent's answers early-game as well as easily removing Shedinja with support from Mold Breaker Pursuit. When switch-ins have been removed, Rayquaza can just spam Boomburst.
Team Options
Imposterproofing is necessary as to avoid a countersweep from Imposter Chansey. The Imposter-countering method will depend completely on the chosen coverage, but either way, Chansey doesn't run Choice Specs, which makes it much more manageable. Fur Coat Chansey can counter Mega Rayquaza's Imposter no matter what coverage is used. Aegislash can counter any variant that runs Fighting coverage with relative ease, and Levitate Registeel can do the same with Ground. A way to beat Shedinja is necessary, so a Mold Breaker Pursuit trapper like Mega Mewtwo X, Giratina, or Mega Gengar is a good teammate. Mold Breaker Pokemon can also set Stealth Rock up without worrying about Magic Bounce, which raises Rayquaza's chance of 2HKOing specially defensive Registeel with Boomburst from 60% to 98%, easing prediction and making revenge killers such as opposing Rayquaza and Imposter Chansey take chip damage. A way to remove Stealth Rock from the field is also incredibly important, as Rayquaza is weak to Rock. A Pokemon that finds opportunities to switch in against most teams can usually use Defog reliably; Giratina, for example, checks most physical attackers and is able to use Defog. Steel-types and -ate checks, such as Registeel, Aegislash, and more specific Pokemon such as Magic Guard Ho-Oh and specially defensive Tyranitar, are also reliable Defoggers because of the prevalence of Rayquaza and Diancie in the metagame. RegenVest users such as Metagross and Zekrom can also use Rapid Spin but are less reliable due to Ghost-type Pokemon like Giratina being immune to Rapid Spin. A Magic Bounce Pokemon can also help at preventing hazards altogether, though a Defogger should still be run alongside it in case of a mispredict or Mold Breaker user. Ways to bait and beat Chansey are not at all necessary, but appreciated; these include bulky Pokemon with a trapping move that can make Chansey struggle to death, some Magnet Pull combination like the common Dialga + Xerneas core, or a Steel-type with Volt Switch and a Magnet Pull Ground-type.
