$re = '/username": "(?<username>[^"\\\\]*(?:\\\\"[^"]*)*)"/m';
$str = '..."members": [{"id": "0", "username": "User 1", "discriminator": "0000", "avatar": null, "status": "online", "deaf": false, "mute": false, "self_deaf": false, "self_mute": false, "suppress": false, "channel_id": "0123456789", "avatar_url": "https://..."}, {"id": "1", "username": "User 2", "discriminator": "0000", "avatar": null, "status": "online", "game": {"name": "pls help"}, "avatar_url": "https://..."}, {"id": "2", "username": "Bot 1", "discriminator": "0000", "avatar": null, "status": "online", "game": {"name": "music | ;;help"}, "deaf": false, "mute": false, "self_deaf": false, "self_mute": false, "suppress": false, "channel_id": "1234567890", "avatar_url": "https://..."}, {"id": "3", "username": "Use\\"r 3", "discriminator": "0000", "avatar": null, "status": "online", "deaf": false, "mute": false, "self_deaf": false, "self_mute": false, "suppress": false, "channel_id": "2345678901", "avatar_url": "https://..."}], "presence_count": 4}';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php