Hey! It's been a little over a week since somebody last posted, so I thought I'd liven up the thread again. I feel that Double Posting is a necessary evil in this scenario.
Mega Typhlosion
Type: Fire
Ability: Drought
HP: 78
Attack: 84
Defense: 93
Special Attack: 159
Special Defense: 100
Speed: 120
Typhlosion, on paper, should be a great Pokemon. It has a fire immunity and access to the fastest Eruption in the game, theoretically allowing it to do massive damage. In practice, the poor thing gets worn down too fast from entry hazards to use full-power Eruptions and just isn't strong enough without Eruption, on top of a shallow movepool and lower-than average bulk. As a result, it's stuck in a competitive limbo, too strong for NU but far too outclassed for RU. That's what this mega seeks to change. While it may seem outclassed by Mega Charizard due to both being Fire-type Megas with an equal Special Attack and Drought, it has two edges over its competition: Eruption and better speed. This speed lets it get to 372 base speed with a Timid Nature and max EVs, allowing it to speed tie with Alakazam, Dugtrio, and Shields-Down Minior; this means it gets the jump on foes that Charizard couldn't dream of touching, like Terrakion, Choice Scarf Tyranitar, Mega Metagross, and Garchomp, to name a few. Of course, it lacks Charizard's vast coverage options, and still has two massive flaws in meh bulk and vulnerability to all hazards, so you might want to build a team to support it.
Krakatoa (Standard)