1) a) to restrict the mark chosen b) because you need light before this can make it prismatic c) because it is in the art.
2) ... is this a roleplaying/lore question? someone else can come up with a creative answer to this, its really not my thing. and considering you can change your element/mark every match, it seems kinda irrelevant.
3) fractal + sparks + SoP was a three card combination, that is now a four card combination, so the draws will be even less consistent and harder to pull off.