What does the fifth power up do?
Viewing post in Minesweeper, but with Powerups comments
That one makes powerup tokens stick around 'til the next game if you win. By default they get cleared. I know, it's rather harsh especially considering the rarity of winning multiple games of minesweeper in a row. I'm currently working on an update which will make it much cheaper since it's way overpriced.
(Incidentally, I'm rebalancing and tweaking nearly all the powerups for the next update right now. There will be approx. 10 instead of 7, have more variety, and will be generally more powerful for the price / cheaper.)