Description (From Bulbapedia): Gives the holder immunity to Ground-type moves, but pops when the holder is attacked. Indirect damage will not pop the balloon, and neither will Ground-type moves used against the holder. The holder is also not affected by Spikes or Toxic Spikes. The balloon will not work if Gravity is in effect.
Air Balloon is simply one of the most prevalent and practical items in the Dream World OU metagame. Remember the old Standard OU tier when Excadrill ran rampant? Many Pokemon were given usage / not given usage due to their ability to handle the mole. In Dream World, Excadrill is more prevalent than ever, and sand is nearing 60% usage on all teams in 1337 range. Another plus to the use of Air Balloon is the resurgence of Garchomp—a Pokemon banned in Standard OU—as it is arguably one of, if not the, best sweepers in Dream World. I'll attempt to list the uses and head a discussion around one of the best items in the metagame.
Pokemon that Benefit from Air Balloon
Excadrill @ Air Balloon | Sand Rush
Jolly | 252 Atk / 4 Def / 252 Spe
Earthquake | Rock Slide | Rapid Spin | Swords Dance
Excadrill: Yea, this is a bit ironic, but it is really easy to explain the practicality of Air Balloon on Excadrill: the mole gets a temporary immunity to opposing Excadrill and can check opposing sand teams quite well. While it is a one time use item that does not provide the power that Life Orb grants, it does well anyways considering that Excadrill already has a fantastic boosting option in Swords Dance and double its normal Speed under the sand.
Ninetales @ Air Balloon | Drought
Jolly | 252 SpA / 4 SpD / 252 Spe
Sunny Day | SolarBeam | Fire Blast | Will-O-Wisp
Ninetales: Ninetales is a good user of Air Balloon due to its ability to switch in on an Excadrill Earthquake and outspeed and OHKO standard Excadrill. I would say that Air Balloon is pretty useful here, no?
Heatran @ Air Balloon | Flash Fire
Timid | 252 SpA / 4 SpD / 252 Spe
Hidden Power Ice | Earth Power | Fire Blast | Stealth Rock
Heatran: Heatran is an amazing anti-metagame Pokemon for its ability to check Garchomp, Excadrill, and other Pokemon that would normally threaten it. With an Air Balloon, Heatran can switch in on any Earthquake and simply OHKO Excadrill with Fire Blast or OHKO Garchomp with Hidden Power Ice. Additionally, it serves as a great makeshift check to sun teams, though admittedly Blaziken will still mow through it. Also, it works as a great option for teams that need a Chandelure counter, as Chandelure is not going to touch Heatran unless it carries Hidden Power Fighting or Hidden Power Ground, two somewhat rare options (Hidden Power Ground only works when Air Balloon is broken!).
Discuss
What do you guys think about Air Balloon? Discuss possible uses / things I left out / why it's useful or not useful. I think it's one of the best items in the metagame due the prevalence of sand abusers, and with the current metagame, it should remain that way.