Sigilyph @ Flame orb
Trait: Magic Guard
EVs: 252 HP 16 Def 240 SpD
Calm Nature(+SpD, -Atk)
- Cosmic Power
- Psycho Shift
- Roost
- Stored Power
Sigilyph has a movepool that gives it fantastic coverage for offensive teams. Cosmic power will negate a lot of damage from threats such as Gyarados and Starmie. Psycho shift with the flame orb allows it to break a lot of physical sweepers, roost allows it to regain health, as well as take away super-effective damage from moves such as stone edge(as long as it's in the same turn) and stored power allows it to strike hard after 4 or more cosmic powers, at least 2HKO-ing special walls.
Tactic:
Send it on the field when there is a wall on the other side. Your opponent will probably switch, because the flame orb will prevent status effects like toxic, and it has magic guard anyway. When this happens, set up a cosmic power. This will prevent an OHKO from common threats like Gyarados. If your opponent sends in a physical sweeper, use a psycho shift to pass down the burn and negate damage from physical attacks. If your opponent sends in a special wall, set up another cosmic power. By now, you should have the stat boosts you need, so roost off any damage taken. Keep setting up cosmic power, and roosting off again. When you feel like you have enough cosmic powers up, start using stored power. This will do VERY high damage, despite the lack of offensive EVs.
Things to watch out for:
Skarmory, Hippowdon, and other Pokemon likely to have dragon tail, whirlwind or roar. This will phase out your sigilyph and make it useless, so make sure these Pokemon are down before using Sigilyph.
To sum it up: Sigilyph is a massively threatening wall when it has a few cosmic powers up, and destroys physical sweepers. However, it does require a good amount of prediction to be used properly.