The bonus is triggered by landing at least 3 coins to award 8 free spins, 4 coins for 15 free spins, and 5 coins for 20 free spins.
Reel Power just means you win by having matching symbols in reels in any position from left to right, generally 3 although sometimes 2 for the top symbol. In Buffalo, the game uses Aristocrat's 'Reel Power' feature instead of just having line pays. It's notable for a few reasons: First of all it's actually my first Buffalo slot video! The 'Buffalo' brand from Aristocrat is one of the most popular slot brands with countless versions such as Buffalo Gold, Buffalo Collection, and of course just plain Buffalo. The Wonder 4 Buffalo slot machine, Special Edition, by Aristocrat is notable!