Just a small little tidbit I noticed while killing some time; every time you destroy the TH in the Goblin mission "Payback" you gain 1 XP. Obviously this isn't necessarily time efficient, but anyone with an Archer Queen or a minion or two can quickly and cheaply gain one xp whenever they're bored.
Just a random little find that I didn't know about for over a year, thought I'd let you all know.
Goodluck on your next "Next" :)

