The smoke bombs were another example of his combined magics. Even though more than combined magic they were actually a smarter use of combined properties.
For example, after his fights with Amelia, Roy knew that the moment that his Acidic Balls came in contact with her Sword Energy it would create a large amount of smoke.
Furthermore, he could also store an amount of Sword Energy from her attacks, and then use it as a one-time attack against her.
But since he was able to store this type of Energy then empty Beast Cores that were left after he had sucked them dry should technically be able to do the same as well.
It was precisely these thoughts that had pushed him to try and transfer the Sword Energy he gathered from Amelia into those Beast Cores, and realize that it wasn't only technical, but also realistically possible.
