I use a google search and look through about 10-20 and pick one I like the most. Also try to make it fit thematically with the changes I makes to it.
As for Froslass, it doesn't have a wide variety of coverage like Gengar, and doesn't have set up moves like Gothitelle. It's weak to rocks, has no recovery, and its not particularly bulky. So it's life span isn't that great.
Empoleon [Water/Steel] (Defiant)
84/86/88/111/101/60 (530)
Mega Empoleon [Water/Steel] (Bulletproof)
84/96/118/121/141/70 (630)
Mega Empoleon @ Empoleonite
Ability: Bulletproof
EVs: 192 HP / 252 SpA / 64 Spe
Modest Nature
- Agility
- Ice Beam
- Hydro Pump
- Flash Cannon
Stats
HP: 357 - Attack: 206 - Defense: 272 - Special Attack: 375 - Special Defense: 318 - Speed: 192
The specific speed EV's allows it to outspeed everything up to and including Weavile that could threaten it after setting up an agility. This is a relatively straightforward Bulky Offensive set and the nice perk of Bulletproof which fits thematically makes it immune to attacks such as Seed Bomb, Bullet Seed, Aura Sphere, Focus Blast, and Shadow Ball.
252+ SpA Empoleon Ice Beam vs. 0 HP / 4 SpD Serperior: 214-252 (73.5 - 86.5%)
252 SpA Life Orb Serperior Leaf Storm vs. 192 HP / 0 SpD Empoleon: 142-169 (39.7 - 47.3%)
252+ SpA Empoleon Flash Cannon vs. 0 HP / 0 SpD Weavile: 314-372 (111.7 - 132.3%)
252+ SpA Empoleon Ice Beam vs. 96 HP / 0 SpD Assault Vest Tornadus-T: 150-178 (46.4 - 55.1%) -- 63.7% chance to 2HKO
252+ SpA Empoleon Ice Beam vs. 96 HP / 0 SpD Assault Vest Tornadus-T: 150-178 (46.4 - 55.1%) -- guaranteed 2HKO after Stealth Rock
0 Atk Tornadus-T Superpower vs. 192 HP / 0 Def Empoleon: 150-178 (42 - 49.8%)
252+ SpA Empoleon Ice Beam vs. 0 HP / 0 SpD Breloom: 310-366 (118.7 - 140.2%)