I like the idea of using a game to encourage people to stick with the pomodoro cycle. Having something to do can certainly encourage people to be more willing to stick with it, rather than just thinking they have to take a break, with nothing planned. Plenty of people play mobile games with a timer limiting their actions, and check back as soon as the time is up to do their next thing, so I could see this working well for them.
I like the idea of being able to shrink it down and dock it to a corner, but even the small size could get int the way. It would be nice if you could also add a tray icon option for when you need your full screen, but also want to know when time is up. It could be a simple icon and a counter. Perhaps have an option of what to display, such as time remaining or amount of mana. Similarly, showing a notification (as an option) would be helpful.
I had a notable freeze when I finished the tutorial. I am on Linux and played this in Wine, so that may have been part of it.
If I click to create a goal, I do not see a way to cancel it. I can get out of the screen by clicking on one of the other buttons at the bottom, that are barely visible beneath the create goal pop up. I was in windowed mode, so maybe that affected the size and position, but the create goal screen is bigger than the previous and covers most of the bottom buttons for me. When I come back it is still on creation, rather than the list. I added one and could then remove it. It also looks like you can only have one goal at a time. It also looks like you can add goals of any length, then mark them completed immediately, to get lots of coins.
After I had 5 mana I went to do more, and did not know what to do next. It would be nice if there were tooltips over the items you can buy to explain what they are and do. Is everything just decorations?