Three more notches on my belt, and that brings me to a whopping 300 Pokémon at level 100! For the last three, I trained them in Y, which is why it's in this thread, and not the ORAS one. I'm a bit late on making this update, because I wanted to figure out the best way to write it, so that it didn't look spammy or taking up too much space.
I was bored of the path I was taking in Omega Ruby, so I moved my last three Pokémon over to Y, in hopes of changing up the formula a bit. I used the Lumiose Restaurants since they're easily the best places to level up. These are the Pokémon I leveled:
#298: Giratina, Altered Forme
Nature: Hardy (Neutral) • Ability: Pressure • Item: Leftovers
Move Set: Shadow Force • Dragon Claw • Protect • Substitute
#299: Sips, the Therian Landorus
Nature: Modest (+ Sp. Attack / - Ph. Attack) • Ability: Intimidate • Item: Assault Vest
Move Set: Earthquake • Fly • Outrage • Hammer Arm
#300: Mega Diancie
Nature: Brave (+ Ph. Attack / - Speed) • Ability: Clear Body / Magic Bounce • Item: Diancite
Move Set: Diamond Storm • Moonblast • Gyro Ball • Stealth Rock
The builds I ended up going with were pretty straightforward. I won't get too into the details of each particular build, since this isn't the place for it, suffice it to say they should all be relatively obvious. There are a few things that might require a bit of explaining, but everything is fairly straightforward. Yes, Sips is using Fly, since it's a powerful hit that let's him avoid almost all damage. In fact, when a Pokemon Flies, they're still vulnerable to a handful of moves, but the one that poses a real threat is Thunder. However, being a Ground-type, Sips is actually immune to Thunder. I didn't level Diancie with her Mega Stone, since Mega Diancie doesn't exist in Y's data. Gyro Ball is a great choice if I use it before Mega Evolving Diancie, and the other two become extremely powerful when I do.
Training was a bit rough at first, being around ten or so levels below my opponents. I immediately went to Restaurant Le Wow, figuring that I would test my strength, and see if I needed to dial it back a bit to Le Yeah first. I took full advantage of everything I could, for the sake of speed. Trade Boost, Lucky Egg Boost, Amie Boost, Triple Battles, Experience O-Power Level 3 ... I was getting some insane experience per battle. Upwards of 50,000 per battle, and thanks to Le Wow being so fast, I only struggled through the first one.
I situated my party so that Diancie was on the far right side, where the weaker enemy is usually opposite me. On the far left, I had Giratina, who is capable of tanking pretty much anything that can be thrown at him, including a full-on Blizzard from Milotic. In the center, I had my main offensive Pokémon, my Therian Landorus named Sips. I mainly stuck to using Fly, but as the levels went on, I could almost clear the entire fight in one move using STAB Earthquake.
With my overall count now at 300, it's time to begin my replay of Heart Gold. Tune into the Recent Happenings for Fourth Gen if you want to follow along.