Right Before You Hit Space Age, Some Aliens Show Up And Ask If You Will Give Them Some Nuggets.
Feel Free To Accept Their Requests Or Ignore Them, Until They Ask For ALL YOUR NUGGETS.
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At This Point, Tell Them No.
- They Will Eventually Start Attacking You.
- Surface-To-Air Missle Defense Towers Are Enough To Stave Off The First Few Invasions.
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They Will Eventually Send Down A Kraker (Boss Battle)
- I Hit It With Lightning Like 15 Times And It Exploded.
- It Seemed SAM Missles Do A Good Amount Of Damage To It Too.
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Once You Defeat It, The Acheivement Pops.
Good Luck!