on endless levels you need to destroy the caves from which the creeps come. If you wait to long the creeps will win. Try buying bombs and destroy the cave.
in endless levels u need to destroy the cave. on lvl. 5 it don´t needs longer than 10-15 waves.... You can upgrade each crystal with up to 3 elements of the same type.... Lvl 4 is verry easy just place a tower in the middle of the path and upgrade it with fire or earth...
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