This might be impossible to put in the game at this point, but it would be awesome to have some secrets or easter eggs to find. Example: Secret paths on the map that don't have arrows but if you press the direction it could be a hidden world/side event. Or walls in the levels that you can walk through to a hidden room perhaps?
I freaking love this series! Even did the beta test when you had that up. It's awesome how you are improving the game as people recommend new implements. Keep up the good work!!! :]
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secret quest