Just logged into Angelic Acid and there was an XP cache in my inventory. I used it about 8 times and got over 5m xp in different stats. Strange thing is, none of my other accounts received this XP bonus. Maybe its an NXT thing? Has anyone else benifited from this mysterious xp cache? Any help is welcome.

It is apparently a gift for playing at least 10 hours on DarkScape before its close. Nice way of them to say thank you :P

 

 

The XP cache is an item given to players who had played at least 10 hours of DarkScape prior to its closure announcement on 29 February 2016. It grants 50% of the experience they gained on their DarkScape character.

 

http://runescape.wikia.com/wiki/Xp_cache

I see, that covers the 50% bonus xp that members paid for in DS...