Truly Amazing Game!
Tips for those that are stuck:
Creating a level 3 piece creates a better item on the top right of the item box (use that before creating another level 3 piece).
Sometimes it is better to have two level 2's than a single 3.
Without money houses, optimal buying is for 1 reroll and 3 pieces.
Don't freeze to much in the early rounds. You want have the option to buy better pieces.
Always get the first book and use to replace the shield.
Use your first book as soon as possible in the round since it triggers by movement.
Wait to use your 2nd (skeleton) book for the row that needs it.
If you don't need to use the skeleton book, then don't. That way you can delay seeing the final boss.
Don't buy the 3rd book.
The Final Boss:
Final boss is always in the middle. Have your best pieces there since as long as you kill the king you technically win.
Before the final boss, sell all your buildings and any useless pieces.
Use the 1st book on any enemy shield pieces in the second row (or if you are definitely going to win, use it on his two knights).
Specifically:
Assassins behind tanks with shields = win.
Stone thrower > Archer since they only attack their column (more predictable) and upgraded stone throwers continue to throw.
Make a single row for summon/summoners = win.
Money house = win.
Like @El_Makina, the shield item is overpowered.
Don't buy the 3rd book or the wizard piece.