Completing the families allow you to unlock more items that can randomly spawn on the levels. Perseverance will give you +1 live at the start of the game but won't make G.I. appear when you play.
Same with the Eye of the tiger. But that complete any families, you'll just have it in your fridge.
Nope, the giant crystals don't count towards the regular items. They are just a token of how great you are

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I bet just like every game on Muxxu it will start with the French and later it may be released on the English one as well.