Gliscor (F) @ Yache Berry  
Ability: Hyper Cutter  
Level: 50  
EVs: 252 HP / 4 SpD / 252 Spe  
Careful Nature  
- Taunt  
- Earthquake  
- Fire Fang  
- Roost

This Gliscor set is made specifically to deal with setup and stall Pokemon. Taunt prevents your opponent's Pokemon from using all setup and status moves for a few turns. That means no Double Team, no Toxic or Thunder Wave, no Confuse Ray or Swagger, no Curse or Calm Mind, no Recover or Rest, and no Trick Room. Any setup or stall move or strategy that's given you grief in the Battle Tower and Taunt shuts them down completely. Pokemon that revolve around these sort of strategies become much less of an influence in battle. There's even a significant chunk of Pokemon in the Battle Tower that ONLY run setup and status moves. So by Taunting them, they're reduced to only using Struggle, which will make them lose 1/4 of their health every time they attack. By the time their Taunt wears off, the opponent's Pokemon have likely lost most of their HP and can easily be taken out by you and/or your partner (since they're programmed to have their Pokemon attack the weakest target on the field). Now of course, you're not always gonna go up against opponents who utilize setup or stall strategies. So I needed my Taunt user to be a Pokemon that still maintains an offensive presence in battle. After a long search, I came to realize that Gliscor was the ideal candidate for this strategy I was experimenting. It's fast, relatively bulky, and has a great typing that gives it immunity to Thunder Wave and other Electric-type moves. Earthquake gets STAB, and can hit both of your foes' Pokemon (make sure to pair with an ally that's either a Flying-type or a Pokemon with Levitate so they aren't hit by Earthquake as well). Fire Fang is a single-target move that gives Gliscor great coverage overall. There's also the chance it can cause foes to flinch or better yet burn them. Lastly, Roost helps give Gliscor longevity. Best of all, it temporarily removes its Flying typing, which gives it only a 2x weakness to Ice-types rather than a 4x weakness. Maximizing HP and Speed with a Careful nature is very effective when combined with Gliscor's natural bulk. The Speed investment is necessary to maximize Taunt's effectiveness, enabling Gliscor to shut down a majority of Pokemon that run setup and stall moves before they can even use them. Yache Berry can enable Gliscor to tank at least one super-effective Ice-type attack. While you normally want Gliscor to avoid battling Ice-types as best you can, there are a few that run some stall or setup strategies that you'll want to shut down with Taunt before switching out. Thankfully the Yache Berry makes that possible. Lastly, you'll want Gliscor to run the ability Hyper Cutter. Since Gliscor doesn't have any attack EV investment, Hyper Cutter will prevent its damage output from being dampened by any Intimidate user you may come up against.
Empoleon (M) @ Shuca Berry  
Ability: Torrent  
Level: 50  
EVs: 252 HP / 252 SpA / 4 SpD  
Modest Nature  
IVs: 0 Atk  
- Hydro Pump  
- Flash Cannon  
- Ice Beam  
- Grass Knot

Now the biggest threat to Gliscor is Ice-types. So to deal with them, I needed a Pokemon that could not only handle them, but also any Water-types that often run Ice Beam or any other kind of Ice-type move. After much searching, the only Pokemon I could find that best synergizes with Gliscor is Empoleon. Its Water/Steel typing gives it x4 resistance to Ice-type moves and its movepool enables it to handle both them as well as opposing Water-types. Should you ever go up against an Ice-type Pokemon or something with Ice Beam, switch Gliscor out immediately and have Empoleon deal with them. Hydro Pump is Empoleon's strongest STAB move, the move isn't very accurate but its Empoleon's only special Water STAB option in this Gen. since Surf now hits your ally in Double battles. Flash Cannon is Empoleon's secondary STAB option. While the move may feel unnecessary, it is vital for dealing with the Ice-type Pokemon that threaten Gliscor. Ice Beam gives Empoleon solid neutral coverage as well as a means of dealing with Dragon-types that Gliscor really can't handle with its moveset. Lastly, Grass Knot is meant to deal with Ground-type as well as opposing Water-types. Most notably the move handles Water/Ground-types that can threaten both Gliscor and Empoleon like Quagsire, Swampert, Whiscash, and Gastrdon as a single Grass Knot is often enough to OHKO them. Max HP and Special Attack investment with a Modest nature enables Empoleon to tank hits and dish out hits the best it can. Having it hold a Shuca Berry enables Empoleon to tank at least one super effective Ground-type that would otherwise OHKO it. Best of all, you can preserve it by switching Gliscor back in, which is immune to Ground-type moves. Lastly, Torrent is Empoleon's only available ability in Gen. 4. Something important to note about Empoleon is that it is not very fast and will more often than not be moving after the opponent. So keep that in mind in case you need to pivot Gliscor back in.  
* IMPORTANT TIPS TO KNOW*
Because this team primarily revolves around utilizing Taunt, knowing exactly what Pokemon sets your opponents are using is an absolute necessity. So with this mind, you're gonna want to look up trainers and what Pokemon sets they specifically run in either of the Gen. 4 Battle Tower on either Bulbapedia or this other site I use called Psypokes. Things will get much more difficult if you try a blind run with this team. 
The ideal AI trainers you'll want to pair with are Mira or Riley (mostly Mira). Cheryl can occasionally run good Pokemon too so check her out every now and then. But ultimately, Mira is the trainer you want to have as your partner as her Pokemon selections synergize well with Gliscor and Empoleon. You should often be fine with whatever she has early on in a streak. But by Battle 35, you'll want her to run either Moltres, Togekiss w' Heat Wave, or Heatran (just don't have Gliscor use Earthquake anytime they're out on the field together). The reason I mention this is because my experimental team has a hard time dealing with Steel-types, specifically Metagross and Bronzong. Both can tank Gliscor's moves relatively well and Empoleon's Hydro Pump is the only move it has that can hurt them. So having your AI Partner run a Fire-type or something with a Fire-type move that can help you better deal with those Pokemon that can end up being problematic.  
Something important to note is that Gliscor can have a hard time tanking special hits. It strongly depends on the Pokemon you're up against, but if their special move got rid of almost or over half of Gliscor's HP, you'll want to switch Gliscor out next turn. Empoleon has high special defense, so it can tank special hits easily. If you have an Empoleon up against either a Fighting or Electric-type, switch Empoleon out and Gliscor back in as it will better be able to tank or just be immune to the incoming attack.