Moolah Picchu is part of Konami's “Passport to Riches” family of slots featuring MultiMystery Xtra Reward upgrades, which are randomly awarded and can also occur in combination with each other, and that’s where the real fun begins:
Free Reels: Randomly, a second set of reels are used on the top screen for an individual spin. The reels and lines that are shown on the top screen are the same reels and lines that the bottom screen uses.
Wild Feature: Randomly, during the reel spin, Action Stacked Symbols change to the wild symbol. (Action Stacked Symbols is a feature of the game where before each spin, certain reel positions are randomly replaced with the same symbol, giving you a better shot to “Fill the Screen” with that symbol).
XL Wild Reel: Randomly, after the reels stop, extra wild reels spin over the existing reels, potentially adding special wild symbols to the outcome.
The Free Games Feature is triggered by landing 3, 4, 5, or 6 or more bonus symbols for 15, 20, 30, or 60 free games respectively. During the bonus, all wins are doubled.
Obviously, the Holy Grail is to trigger all MultiMystery Xtra Reward features during the bonus for that Big Win or Jackpot. One final point to note is that these upgrade features do not come for free, as half of your bet pays for them, Enjoy!