Do yourself a favor and do not watch this. Instead, go read a walkthrough for this stage or even better, Ill list the locations right here in the description! That way you wont see me sucking hard.\r
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The custom balls are in hidden rooms. To get them, simply hug the walls. One is in the ground above the door near the accumulated snow in the first screen, the other is in a hidden room in the second level of the next screen. As for gold cards, one is in the other hidden room, in the alternate second screen; the other is behind that infamous tree guarded by one of the ski houses.