You can no longer do online battles with 5th gen cartridges since WiFi for DS (and Wii) games was shut down in like May 2014. The only games that can do battles with other people these days are the 6th generation games: X, Y, Omega Ruby, and Alpha Sapphire.
The 5th generation meta does still exist on Pokemon Showdown, thouhg idk how many people play it. If you wnat to get into the 6th gen meta,
Smogon has some resources to view, and the people here on PC are willing to help you out too.