Thank you playing the demo, the "more thunder " options increase the frequency of the lightning strike landing on the screen, but every time you choose the option is less powerful, in future updates I will limit the amount of times this power up appear.
Also some more descriptive card descriptions would be great too or perhaps even a way to see your stats while ingame.
Of course, those are planned features, upgrades will have their own icons and description will appear as you select the powers.