Despite the likes of Mega Charizard and Mega Mewtwo often stealing the headlines, there are actually far more gen 3 Mega Evolutions than there are gen 1. In fact, gen 3 Mega Evolutions make up almost half of the total Mega Evolutions in the entire Pokemon series; at least at the time of writing, anyway. While there are certainly some powerful Pokemon amongst this number though, quite a few of them are underwhelming to say the least.
Total base stats may play a big part in making a Pokemon great, but the way that those stats are distributed is also incredibly important. Without the right balance, a Pokemon might not survive long enough to fully utilize its biggest strengths or, conversely, it may lack the firepower to finish off its foe even if it's durable enough to last those few extra turns. With that in mind, the Hoenn region really does offer something of a mixed bag.
20 Mega Camerupt
While Mega Camerupt is incredibly strong in the special attack department and has a decent physical attack stat as well, its ridiculously low speed makes it a little difficult to use in competitive battles. It's all but guaranteed to act second and, with its defensive stats both around 100, is liable to being knocked out by a single weakness exploiting attack. If it does manage to survive though, it can at least deal some decent damage; especially when using moves with additional effects.
19 Mega Banette
Mega Banette doesn't quite fit the description of a glass cannon, but it's not too far off. Its 165 physical attack stat has the potential to be devastating, but whether or not that potential is ever fully realized will likely come down to the opposing Pokemon's speed. 75 isn't terrible, but given that most Pokemon used competitively have speed stats of 100 or higher, Mega Banette is going to be acting second more often than not.
18 Mega Altaria
Mega Altaria is an incredibly well balanced Pokemon in every department except speed. Sadly, in a world in which most of the top tier Pokemon tend to excel in either defense or offence, it's difficult to see where Mega Altaria really fits in. In all likelihood, it's either going to lack the firepower needed to go blow for blow over the course of a long battle or get instantly knocked out by a Pokemon with a high special attack stat.
17 Mega Glalie
Unlike Mega Altaria, Mega Glalie at least has its strengths. These come in the form of its high special and physical attack stats and are balanced out by some fairly weak defenses. Ultimately though, it doesn't quite lean far enough into this division to really stand out.
When all's said and done, Mega Glalie just doesn't have enough firepower to be able to reliably take out its foes in a single hit, but then nor is it likely to be defeated by one either. As a result, it's a fairly average Mega Evolution.
16 Mega Sableye
With just 20 speed, Mega Sableye is the joint slowest of all of the gen 3 Mega Evolutions and is also tied for the lowest base stat total. Despite its slow speed, however, it boasts a fairly solid defense and its Mega Bounce ability can be incredibly useful for dealing with entry hazards too. When paired with Recover it can be a useful staller, but due to its lackluster offense, Mega Sableye can sometimes lack the bite to deal with bulkier teams.
15 Mega Sharpedo
A 105 speed stat may not seem that great, but thanks to Sharpedo's Speed Boost ability, Mega Sharpedo is faster than most Pokemon by the time it enters the fray. This bodes well, as its poor defenses make it vulnerable to being knocked out by a single blow. It makes up for this somewhat though with its 140 physical attack stat and its Strong Jaw ability, both of which help it to deliver one hit KOs with Crunch fairly consistently.
14 Mega Absol
Mega Absol has a fairly similar build to Mega Sharpedo, although boasts higher speed and a higher physical attack stat. This does come at the cost of defense, but assuming it acts first and is able to attack its enemy's weakness, there's a very good chance that Mega Absol will be coming out on top. If that first hit isn't a knockout though, it may not survive for too long.
13 Mega Mawile
With its low base stats and abysmal speed, Mega Mawile really doesn't have too much going for it at first glance. Thanks to its Huge Power ability though, it effectively has an attack stat above 200; allowing it to dish out a lot of damage when given the chance. Sucker Punch can somewhat make up for its slow speed too, but this strategy can leave the Pokemon vulnerable to revenge kills.
12 Mega Medicham
Mega Medicham's 510 base stats may not seem all that impressive, but its Pure Power ability more than makes up for this. Like Huge Power, Pure Power doubles a Pokemon's attack which makes Mega Medicham incredibly deadly in certain situations. Its 85 defenses can leave it a little vulnerable, but its 100 speed and access to Fake Out help to mitigate this somewhat.
11 Mega Gardevoir
Mega Gardevoir has an incredible 165 special attack stat and backs this up with solid special defense. In the right situations, it can therefore be incredibly effective and should have the beating of most Pokemon that rely on special attacks and physical defense. It also boasts a strong learnset that includes many of the best psychic and fairy-type moves; the overwhelming majority of which just so happen to be classified as special attacks.
10 Mega Swampert
Despite having slightly higher total base stats than the Mega Evolved forms of the other two gen 3 starters, Mega Swampert is arguably the weakest of them all. It does have a very impressive 150 physical attack stat and solid defenses too, but its low speed means that it's likely to be acting second in most encounters. Of course, depending on the Pokemon that it's up against this might not be an issue, but unless it has type advantage it may not last long enough to really make the most of its devastating physical attacks.
9 Mega Manectric
Like many electric-type Pokemon, Mega Manectric has very high speed and special attack stats. Both are 135 and its base stat total clocks in at a fairly impressive 575. There are certainly stronger Pokemon out there, but Mega Manectric should have enough in its arsenal to take care of most flying and water-type Pokemon fairly comfortably.
8 Mega Blaziken
Not only does Mega Blaziken have a higher physical attack stat than Mega Swampert, but it's also much faster too and its Speed Boost ability allows it to become faster still as battles progress. It does fall a little short in the defensive department, although it definitely has the moves to finish a battle quickly if it's able to act first. If not, then it's unlikely to survive for too long.
7 Mega Sceptile
Mega Sceptile may have the same base stat total as Mega Blaziken, but it just edges out its fellow starter Pokemon thanks to its 145 speed stat. There really aren't too many Pokemon out there that are able to match or better it, meaning that Mega Sceptile will be acting first almost every single turn. When it does so, it can utilize its 145 special attack stat which should give it the edge against dragon, ground, rock or water-type Pokemon more often than not.
6 Mega Aggron
How good Mega Aggron is really depends on the opposition. Against Pokemon with high physical defense and a strong special attack it's not that great. When up against Pokemon that rely heavily on physical attacks, however, Mega Aggron really comes into its own.
Its 140 physical attack stat is impressive in its own right, but it's the Pokemon's 230 physical defense stat that really makes it shine. Few Pokemon can go blow for blow with it, especially without the aid of type advantage. Even when they have it, Mega Aggron's Filter ability can really level the playing field.
5 Mega Salamence
Mega Salamence has a lot going for it, with the pseudo-legendary Pokemon's special defense stat being the only one below 120. It's geared more towards physical combat than special, although can still pack quite the punch with special attacks if it really needs to. Some may have perhaps preferred the extra ten points to have gone towards its physical attack stat instead, but, considering its learnset, the base stat distribution does make a lot of sense.
4 Mega Latias
Both Mega Latias and Mega Latios have a total of 700 base stats, but the latter has a slightly better distribution. That said, Mega Latias is certainly no slouch, particularly in the special attack and defense departments. She also has sold physical defense which should give her the upper hand against all but the very top tier Pokemon.
3 Mega Latios
Mega Latios is a bit more offensively minded than his female counterpart, as evidenced by his 160 special attack stat. Despite this, neither of its defense stats are below 100 and its 110 speed should be enough to ensure that it attacks first in most encounters. As such, he excels in shorter fights; which most of the battles involving Mega Latios tend to be.
2 Mega Metagross
Much like Mega Aggron, Mega Metagross largely relies on its high physical attack and defensive stats. Where it sets itself apart though is through its high speed and solid special stats. This makes the pseudo-legendary Pokemon a lot more versatile, albeit slightly less durable. Thanks to its Tough Claws ability and speed, however, it's able to finish its opposition off much faster and so doesn't need to be able to withstand quite as much punishment.
1 Mega Rayquaza
Mega Rayquaza is not just the best of the gen 3 Mega Evolutions, but is arguably the best Mega Evolution, period. Only Mega Mewtwo can match its 780 base stat total and although a theoretical Mega Arceus would surpass it, for now, at least, Mega Rayquaza is right up there amongst the very best Pokemon. It boasts insane 180 physical and special attack stats which is more than enough to wipe out the majority of Pokemon in a single turn. Thanks to its 115 speed stat, that tends to happen quite a lot.