There isn't really anything wrong with your team. Often you go through most battles with great ease and then find one that haxes you out. You might want to swap Lefties on Starmie with Shell Bell, Starmie hits hard and has enough super effective coverage and low enough HP that Shell Bell outclasses Lefties in the healing department. Personally I also use Modest on Starmie to hit harder, I don't think there is anything of note in the frontier in between Modest and Timid max speed for Starmie. Modest Jolteon still sits slightly above Timid Starmie for example.
Alternatively, you might want to swap Starmie for Latios. Starmie is immune to Attract and has Natural Cure, but Latios has a base 130 Sp.Atk (Starmie only 100) and much more bulk. Latios can run a similar set to Starmie, like:
Latios @ Soul Dew / Shell Bell
Timid / Modest nature
252 Speed, 252 Sp.Atk
Psychic is your primary STAB move, Dragon Claw is a good STAB move that destroys opposing dragons and hits harder than Starmies Ice Beam against the Lati twins and still OHKO's Flygon and Salamence easily (it also OHKO's some variants of Dragonite as well, and all of them with Soul Dew). Thunderbolt destroys the water types that want to try Ice Beam, and Surf is a final coverage move that OHKO's pretty much everything that is hit super effective by it (except maybe Tyranitar and Entei, not sure about those). What makes Latios mainly better than Starmie is that it has the same wide super effective coverage, but with more bulk and better defensive typing. While Latios has 5 weaknesses, only Ice is relatively common coming from water pokémon, and Latios can generally beat them easily one on one with Thunderbolt unless they get a very lucky freeze, as Latios is not 2KO'd by Ice Beam unless it came with STAB. Starmie stays suffering from the fact that most neutrally hitting STAB moves hit it quite hard and that Starmie just doesn't hit as hard as it wants to. 100 Base Sp.Atk is good but not perfect. Oh, and Latios is immune to the infamously cheap Quick Claw + Fissure Wailord that pops up every now and then in the Frontier.
For Agility Metagross, try not to explode immediately. Metagross can be used as a brutal physical wall that just eats up physical attacks (even Earthquakes and Explosions) and punches back hard with Meteor Mash. Explode when it is about to go down, but often Agility-gross can bring down teams on its own, even in later rounds. Also, slightly less speed EV's and ALWAYS Max attack. 405 Attack makes it hit brutally hard and allows it to 2KO opposing Metagrosses with EQ. Go for 180 Speed stat, outrunning modest Jolteon after an Agility, leaving only Timid Jolteon and Ninjask (Lol) to outrun you after Agility.
Slaking I've never used in the frontier, but I guess CB Slaking works really well. You might even want to consider running Hyper Beam as the AI is too stupid to take advantage of you not switching anyways and CB STAB Hyper Beam OHKO's pretty much anything that doesn't resist it.
Last edited by Sceptile Leaf Blade; 18th February 2013 at 8:35 PM.
Master balls are the cheapest thing ever invented. It's more fun catching everything with balls that can fail. 'caught Latios in the wild without master ball ftw'