From the release notes:
[quote:1w94npxn]All Cordova plugins are now fetched from the NPM registry instead of the old CPR (Cordova Plugin Registry). Unfortunately, not all plugin authors have migrated their plugins to the new NPM plugin registry. If you have trouble retrieving plugins from the new registry that were available in the old registry you may have to specify that plugin's GitHub in order to add it to your project.
I couldn't build Crosswalk app with phonegap AdMob (as it is in the C2 AdMob manual). Also couldn't re-add it (even with GitHub url). This plugin is depracated and I believe Cranberrygame will not update this one any more so C2 manual should be probably updated.
Instead I have succesfully added Cordova AdMob plugin to my project in Intel XDK. However there is a known issue that C2 official plugin freezes the screen pretty often when combined with Cordova AdMob library. So again C2 official AdMob plugin probably will have to be updated or removed as there is no longer compatibile plugin in Intel XDK.
I will test now C2 official + Cordova AdMob and see if it still freezes. If so then I'll switch C2 official AdMob with Cordova AdMob in C2 and test again. Will let you know how it goes.