I love this idea, but there needs to be a clarification about the 'up/down' aspect of it.
Looking at the picture before, you have 3 rows (8, 7, and 8 again). In the middle row, next to the two Ice Dragons, there's a Ruby Dragon to the 'lower left' side of one of them. If you used Fire Bomb/Mortar on that Ice Dragon, would it hit the Ruby Dragon? Or would it possibly 'hit' the potential monster to the right of it?
Again, the question is: creatures alligned 'up/down' don't make sense, because the cards are shifted approximately half-way to prevent overlap. So if you target a creature in the middle (7) row, which of the creatures (left/right) does it affect when the area of effect chooses its top and bottom damage areas?