health popups will display your health (and the enemy's too) when in combat or when picking up a potion. The same popup will also, well, pop up when you collect items, money or experience points!
Crates serve as static obstacles that the knight can destroy to make way. In the future, these crates will have a chance of containing items to collect.
As long as 2 of them are present on the board, the warps can swap the positions of everything that steps on them. This includes the player and the enemies as well!