The truth is, if a pokemon trainer were to find out about Barragan's weakness, an Abra could beat Barragan. He can beat the likes of Stark, Ulquiorra, but if Abra uses teleport, he's a goner.
That really says something about how stupid his weakness was.
To beat Barragan, all you need is someone/something that can teleport, or a really, really powerful blast (not including, obviously, reality warping or such other mega powerful abilities).
Another disgusting truth is that if Barragan were to fight any of the vampires from Twilight, it would end in a draw, since anything immortal cannot be decayed by him.