1. Mega Manectric should stay B rank. It takes up the mega slot and doesn't hit hard enough (flamethrower fails to OHKO sp.def Ferro). Volt Switch can be used to scout, but Zapdos can do that too, and it also has access to Defog, Roost and Heat Wave. Also, Mega Manectric is frail even with Intimidate, and it can't do anything about most special attackers, unless they are weak to its STAB. Honestly everything it does can also be done by Zapdos.
Have you tried using Mega Manectric once? I've made a couple of posts about moving it up to A- Rank for a while now. Taking up a Mega Slot is not a viable unless you need to run Mega Zard X for Dragon Dance, or Mega Zard Y for a bit of wallbreaking and Sun Support. Mega Manectric acts a really fast and powerful pivot that really fucks up a lot of things with its high Speed tier (135!!). And are you seriously comparing Zapdos and Mega Manectric? For real? Mega Manectric runs Volt Switch / Hidden Power [Ice] or Hidden Power [Grass] /
Overheat / Thunderbolt. And about the Ferrothorn thing:
252 SpA Mega Manectric Overheat vs. 252 HP / 252+ SpD Ferrothorn: 380-448 (107.9 - 127.2%) -- guaranteed OHKO
and on hazard stacking teams, Mega Manectric can run Flamethrower as well:
252 SpA Mega Manectric Flamethrower vs. 252 HP / 252+ SpD Ferrothorn: 264-312 (75 - 88.6%) -- 50% chance to OHKO after Stealth Rock and 1 layer of Spikes
Here's Flamethrower vs. the set in the analysis:
252 SpA Mega Manectric Flamethrower vs. 252 HP / 40 SpD Ferrothorn: 344-408 (97.7 - 115.9%) -- guaranteed OHKO after Stealth Rock
So, I don't know what you mean by that. And if Ferrothorn has taken any previous damage, it is killed by Flamethrower after Stealth Rock, and even if it is, it's left with what? ~7% HP? Still enough to be killed by anything. It has a base 135 Special Attack, which is higher than Keldeo and Thundurus without boosting items, and Mega Manectric has base 130 Defense
-1 252+ Atk Choice Band Talonflame Flare Blitz vs. 0 HP / 0 Def Mega Manectric: 189-223 (67.2 - 79.3%) -- guaranteed 2HKO
252+ Atk Choice Band Talonflame Flare Blitz vs. 252 HP / 168+ Def Zapdos: 204-241 (53.1 - 62.7%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
Here's just an example, and while Zapdos is far bulkier, do you notice how they're both 2HKOed? Also, notice how Talonflame is stuck with the -1 until it switches. Oh yeah, and the fact it is OHKOed with Thunderbolt (and outsped!!). Zapdos lacks offensive presence, is weak to Stealth Rock, and not to mention the fact it plays a far different role than Mega Manectric, it's a bulky Defogger, while Mega Manectric is a fast offensive pivot. The one thing in common is the access to a VoltSwitch and being Electric-types, it stops there though. Zapdos also isn't guaranteed to OHKO:
68 SpA Zapdos Heat Wave vs. 252 HP / 40 SpD Ferrothorn: 296-352 (84 - 100%) -- 37.5% chance to OHKO after Stealth Rock
So there's that as well, and Mega Manectric's Overhaeat > Zapdos' Heat Wave any day. I also wouldn't call it not bulky:
4 Atk Ferrothorn Power Whip vs. 0 HP / 0 Def Zapdos: 142-168 (44.2 - 52.3%) -- guaranteed 3HKO after Leftovers recovery (with the Flying-type taken away)
-1 4 Atk Ferrothorn Power Whip vs. 0 HP / 0 Def Mega Manectric: 100-118 (35.5 - 41.9%) -- guaranteed 3HKO
It's bulkier than an uninvested Zapdos, while also being much faster and more powerful. I'll give it to you that Zapdos is more specially bulky, but still, you're missing the point of Mega Manectric. It is supposed to just Volt Switch whenever and use coverage when needs be, it's not to be used 'just to scout'. That's like saying you can only eat a small slice of the cake! Try out Mega Manectric, it's amazing for offensive and VoltSwitch teams alike. But I'm not cool with comparing Zapdos to Mega Manectric, when they play different roles. Of course Heatran outclasses Mega Charizard Y defensively, the same can be sad about Zapdos outclassing Mega Manectric Defensively. Now, Diggersby. It's the bane of stall and +2 Diggersby is a gg. I'll get more in-depth later, but I don't want to go into a whole huge thing right now :].