I just recently started playing, and I've reached a point where it's difficult for me to progress in the game, and I'm not really sure what it is that I'm supposed to be doing about it. Every time you beat a level 3 times, it increases the difficulty to a new tier. If that tier is too difficult for me to beat, then what am I supposed to do? Is there no way for me to go back and farm the previous tier, to try to save up some cash and viagra, so I can strengthen my units enough to challenge the current tier? I know that I can move on to another level, but I'm starting to reach a point where those are too hard as well.

On a similar note, it feels like the game expects me to have way more resources than I seem to be able to get. Is there some reasonable way to farm more viagra/cash, that I'm just not aware of? As it currently is, I can't seem to make enough progress in this game that it feels like a rewarding/worthwhile endeavor. If I spend 2.5 hours worth of energy, I can't even get enough cash to research a single combo, or enough viagra to level a card one time.

Yeah, aside from the 8hr free card and progressing to further stages, there's no way to farm earlier stages for cards. Even when you max out the stage you only get cash and viagra.