A few bonus levels in solo, after 150 stars, that are super, rediculously difficult and have dark elixir available as loot in addition to normal loot. Maybe include some exclusive upgrade or decoration for completing solo.
I enjoy the problem solving aspect of the solo missions, so this would be more challenge added to your game. Also, maybe a design contest for players to build new goblin levels and get them approved for new solo levels?
Plus, we need a goblin king. Barbs have royalty, archs have royalty, goblins should have like a king or jester or prince or something.
