Thanks really happy that you liked the game, the art and all :)
well the spin attack could be considered a bit of a hidden mechanic since i didn't really told about it in the controls, but that's not the one i think would be as hiden to discover (even though calling it hidden is a bit of a stretch, i'm just curious to see if people try it if not explained in the controls :p)
i'll give a hint, it is with the brother character, and it involves projectiles.