I've completed all of 'em with using my DS's original cartridge.
But,quite impossible to catch all of em to get those Chasm. For me,it's easier to obtain legends instead of normal pokes.O_O
Really? If I wanted I could catch normal pokemon en masse and still have an easier time than legends like mewtwo, the three birds, the three regis, the biosphere trio, the emotion trio, and the space trio. And as for trade only pokemon, that's really not a problem since I have Leafgreen, Firered, Emerald, XD:GoD, Pearl, Platinum, and White. I could get every single pokemon save for a couple legends and event legends. So getting the pokemon is not a problem, the problem however, rises in the time needed to hard reset the games that I can/want to do so (XD:GoD, Leafgreen, Emerald, and Platinum) and spending that time to beat the game. So unless you don't have a working Wii, 2 GBAs, 2DSes (of any kind), and each of those games, you won't have much of a hard time collecting pokemon for B/W2