Mega Alakazam may deserve to go to A-, because i think it is the best revenge killer available in OU. No need to use weather, a Scarf, or a somewhat weak attacker to cover speedy threats, Mega Alakazam has them covered. What else can revenge kill almost every single offensive threat, including Swift Swim sweepers, Sand Rush Excadrill, Adamant Scarf Landorus-T, Scarf Heatran, Mega Manectric, +1 Gyarados, and +1 Dragonite? Not to mention that even without a boosting item, Timid Mega Alakazam has power equivalent to that of a Timid 123 SpA Pokemon with Life Orb. And on top of this, Mega Alakazam can take advantage of common Pokemon such as Landorus, Heatran (Taunt shuts down Earth Power-less Heatran), Clefable (Unaware ignores Calm Mind boosts and allows Mega Zam to 2HKO it) Thundurus (priority Taunt prevents priority Thunder Wave), and Greninja, to the point of making some of them a liability. Nothing can take on a Sheer Force or Adaptability Mega Alakazam except from Chansey, and even Chansey loses if Mega Alakazam has Taunt.
As long as you MEvolve Mega Alakazam early on the game, you have most speedy threats covered, except from Scarf Terrakion, Scarf Garchomp, Jolly Landorus-T, DD Mega Charizard X, and Scarf Keldeo, all easy Pokemon to take core of with great pivots such as Landorus-T and Rotom-W. Not only this, but Mega Alakazam is a terrific late-game sweeper and hole puncher against all kinds of teams. Hidden Power Ice, Hidden Power Fire, and Taunt are all excellent choices on the last slot that allow Mega Alakazam to get past most of its checks and counters, such as SpD Dragonite, SpD Scizor, and Chansey.
Finally, Mega Alakazam can OHKO a ton of offensive Pokemon, meaning that it can be a great Pokemon to use even in the early-game, unlike some other speedy threats such as Mega Aerodactyl and Mega Manectric, which need some prior damage to OHKO most Pokemon not weak to their STABs. Here are some calcs, excluding Psychic-weak Pokemon:
- 252 SpA Mega Alakazam Hidden Power Ice vs. 0 HP / 0 SpD Landorus: 396-468 (124.1 - 146.7%) -- guaranteed OHKO
- 252 SpA Mega Alakazam Psychic vs. 0 HP / 0 SpD Thundurus: 222-262 (74.2 - 87.6%) -- 93.8% chance to OHKO after Stealth Rock
- 252 SpA Mega Alakazam Focus Blast vs. 0 HP / 0 SpD Excadrill: 464-548 (128.5 - 151.8%) -- guaranteed OHKO
- 252 SpA Mega Alakazam Focus Blast vs. 0 HP / 0+ SpD Heatran: 284-336 (87.9 - 104%) -- guaranteed OHKO after Stealth Rock
- 252 SpA Mega Alakazam Focus Blast vs. 0 HP / 0 SpD Mega Gyarados: 260-308 (78.5 - 93%) -- 37.5% chance to OHKO after Stealth Rock (sure OHKO if Gyarados came in on its regular forme)
- 252 SpA Mega Alakazam Psychic vs. 0 HP / 0 SpD Kabutops: 246-291 (94.2 - 111.4%) -- 68.8% chance to OHKO (sure OHKO after 1 LO round)
- 252 SpA Mega Alakazam Hidden Power Ice vs. 0 HP / 0- SpD Garchomp: 420-496 (117.6 - 138.9%) -- guaranteed OHKO
- 252 SpA Mega Alakazam Focus Blast vs. 0 HP / 0 SpD Mega Tyranitar in Sand: 376-444 (110.2 - 130.2%) -- guaranteed OHKO
- 252 SpA Mega Alakazam Shadow Ball vs. 0 HP / 0 SpD Mega Medicham: 250-296 (95.7 - 113.4%) -- 75% chance to OHKO
The only thing i really hate about Mega Zam is the reliance on Focus Blast, but bad accuracy on coverage moves has never been a good reason to hold something back in terms of viability. Want to hear more opinions about Mega Zam, but i think it deserves to go in A-.