What I find is that HP ice is essentially irrelevant at this point, with Bisharp, Cofagrigus and Florges, Mega-Amphy is given ample room to romp around and cause MAJOR problems. But unfortunately, Gardevoir is still the main threat, closely followed by Diggersby.
252+ Atk Choice Band Huge Power Diggersby Earthquake vs. 252 HP / 252+ Def Mega Ampharos: 440-522 (114.5 - 135.9%) -- guaranteed OHKO (just added this to show that you have no hope of ever taking a hit from this monster)
252 SpA Mold Breaker Mega Ampharos Focus Blast vs. 252 HP / 4 SpD Diggersby: 386-456 (103.2 - 121.9%) -- guaranteed OHKO
Diggersby will usually be faster, and earthquake doesn't miss like Focus Miss.
252 SpA Gardevoir Moonblast vs. 252 HP / 4 SpD Mega Ampharos: 278-330 (72.3 - 85.9%) -- guaranteed 2HKO
252 SpA Mold Breaker Mega Ampharos Thunderbolt vs. 4 HP / 0 SpD Gardevoir: 156-184 (56.1 - 66.1%) -- guaranteed 2HKO
252 SpA Pixilate Mega Gardevoir Hyper Voice vs. 252 HP / 252+ SpD Mega Ampharos: 308-366 (80.2 - 95.3%) -- guaranteed 2HKO
4 SpA Mold Breaker Mega Ampharos Thunderbolt vs. 4 HP / 0 SpD Mega Gardevoir: 117-138 (42 - 49.6%) -- guaranteed 3HKO
Gardevoir laughs at mega-amphy. There just aren't enough stats he can boost to handle her. You either get specially defensive, and tank 1 hit, or go specially offensive, and die. Florges is the main Partner here, sponging a hit, and hopefully throwing a Toxic back. That's the only saving grace. Maybe casting a wish as Gardevoir faints and trying to recover the momentum lost with Amphy. That's one lucky scenario that your opponent doesn't switch out to save additional toxic damage and take out florges.
Opposing Florges isn't a problem with proper team support, and if Toxic is added to the offensive threat, it leaves her having to aromatherapy, leaving you to hit more often. All Whimsicott can do is stall you-- leech seed, maybe sleep or toxic, all of which can be taken rather easily, and (if you're running HP ICE, hit back hard) with Florges as a teammate, taken out rather nicely.
To be honest, I really think my "Clean-up Crew" set works the best for Mega-Amphy.
However, I'd like to edit the EV a little bit. I added a bit of Special Defense, just to ease the pain a bit, As Mega-Amphy will often be taking a hit on the way in. Modest and 100 Special Attack brings it up to a cool 430, which is still enough to do major damage to a team.
Clean-Up Crew V2.
252 HP/ 100 Sp Att / 156 Sp Def
Modest
Thunderbolt
Dragon Pulse
Focus Blast
Toxic/HP Ice
However, it's all about how you want to use mega-amphy. If you don't need Amphy to take special hits at all, then invest all of it in special attack, but be warned that despite it's amazing bulk, that it will be hit... alot. It's typing doesn't do it many justices, and if you can keep it from getting trapped by Ice and Fairy, crank the Special Attack all the way up.
Again I cannot stress enough the power of teammates. Bisharp and Florges are more or less musts. The former posing Fairy and Ice threats, as well as threats to Specially defensive walls, and the latter keeping Amphy (and in turn, bisharp) alive to do their jobs. I recommend a revenge killer, something fast like Choice Scarf Darmanitan or Hydreigon to take out any serious threats, and then let Amphy carve away like a drunk lumberjack with a couple of chainsaws. If you plan properly, and cut away the major threats to Amphy, you can finally see why Jasmine-- a steel type gym leader in Johto-- even loved this monster so.
