Thank you for the feedback man. The Mana is Time, so players have +3 seconds to choose a weapon and attack each turn. The faster you are making your choice, the more time you will save for the next turn :D Maybe we will do a deeper tutorial to explain everything.
We are adding some new stuff we couldn't because of the deadline, make sure to play the new update :D There will come the Solo Mode and new stuff that will make battles last way longer!