Due to its planetary stats:
Surface temp: 460 degrees C
Surface pressure: 94 times that of Earth
Mass of atmosphere: 104 times that of Earth
Atmospheric constituents: 96% carbon dioxide, 3.4% nitrogen, traces of water vapor, oxygen, argon, neon, and sulfur compunds
The amount of oxygen is actually about one-fifth that of Earth's. There is roughly four times as much nitrogen in Venus' atmosphere than in Earth's.
Venus has 100% cloud cover (Earth has about 50%). The clouds are primarily composed of concentrated sulfuric acid. The cloud layer is about 15km thick and exists above 50km in the atmosphere.
The amount of water, when compared to Earth, is negligible.
The Venutian year is 225 Earth days.
The Venutian day is 243 Earth days. Venus' rotation is east to west, the opposite of Earth and the other planets.
No moons. No magnetic field either, most likely due to Venus' slow rotation. (the core doesn't get sloshed around enough).
The terraforming of this world is considerably more difficult, and hasn't been touched on much in the comics as of yet (though she has mentioned siphoning off some of the atmosphere as part of the terraforming process ). Syke has given Flinthoof permission to play with it though...