Collective Might is a good deck to use, as it has numerous cards that allow you to put creature tokens into play. I won't list them all, but I counted at least a dozen different cards that can do this. Having the Parallel Lives enchantment in play doubles the amount of tokens put into play. Simply build up a vast army and then overrun your opponent for this achievement.
If playing offline, this achievement is easily obtained against the Disturbing the Nest encounter. See Auramancer for more information.