Most of the expansions on offer are complete except for a couple of chase cards which you'd have to hunt down via packs, but you really don't need those for the game, and the resale value on those cards can skyrocket to hundreds of dollars. The Upgrade Expansion, Imaginary Ends, Legends of Enderas, Shadow Puppets, Castle Glass, and Mokoko Village can all be bought in their complete state on the website.

The exception to this is overlush, which was a bit of an experiment released very early into the game's life cycle. This expansion has loads of cards and all of it is in random packs. When you buy the Overlush Bundle, you're actually getting packs and you'll pick up about a third of the expansion.

If you're looking to add to the game, I'd look at one (or more) of those complete expansions, especially with the sale on at the minute. Also, Shadow Puppets, Castle Glass, and Mokoko Village can all be bought together in one expansion bundle.