To play with someone on coldbird servers you have to set up either UPNP or what I
wouldn't suggest, use DMZ.
When you're done setting it up. Look up supported games or visit
https://pro.coldbird.net/status/status.xml to see what people are actually playing. Status page is a little deceiving. I think the way it works is
total players - ghosts = people in lobby/match. You have to either wait in lobby for someone to join you or set it up with friends. For example there could be 16 people playing Tekken 6 but only 2 be in a lobby, you won't see them because they are already fighting.
@Sonic Angel Knight In reality I wouldn't call it crowded. Just a bunch of people have the plugin installed and are connected to the internet.