Pressure Stall Zapdos*
Zapdos # Leftovers
Nature: Timid (^Speed -Atk)
~ 252 Speed EVs / 200 HP EVs / 58 Defense EVs
- Toxic / Roar
Note: This set works a kajillion times better if the enemies are already Poisoned, from my experience. (Like Toxic Spikes, or a previous staller using Toxic) Although Zapdos comes with Toxic here, you can replace it with Roar if you have Toxic Spikes. Zapdos needs as much time as possible to set up a Substitute, and with the Speed to do it!
Zapdos can make a pretty good Pressure Staller! Although you can still sweep normally with this set, once you encounter something that bothers you, you can just start Substituting, and Roosting to begin the stall! Thunderbolt is there for the STAB, and just to help finish foes off. Substitute is there so that you can Sub & Roost all day long! :D
Have Toxic if you do not have a team with Toxic Spikes. If you have Toxic Spikes, repalce instead with Roar since you won't need Toxic anymore if they are already poisoned, and to bring in some foes to get them poisoned too!