Boss level...
	Free coins...

On the boss level kill everything including the boss and as soon as the boss turns black press the + for using skillpoints and wait in that menu for dash to collect the gold and items. Your gold didn't double (x2) like it used to do in story mode, but when you start the boss level again, your gold will jump to 30-35k gold at the start, and the gold you collected in the previous round is saved.

To get free coins from ads fast go to the character's menu and tap the purchases icon and the free gold for ad option. As soon as the advert appears press the home button and lunch the game again. The advert will be counted as watched and you won't have to spend 30 seconds watching ad for gold.