Okay, let's simplify the text on here first:
- Cast only before blockers are declared
- X can't be more than the number of snow lands you have
- Attacking player pays either 2 (nothing happens), 1 (Deftblade Elite's ability), or 0 (Murder) for each of X attacking creatures. The corresponding effect happens to that creature.
Now that that's out of the way, let's look at the card itself. First, the "X can't be more than the number of snow lands you have" thing. In a deck built around this, that is not a problem since snow lands are still basic lands and therefore you can easily have all your lands be snow. As for the rest of the card, it's not bad at all. Blue doesn't have very many sources of destroying creatures (Pongify is the only one I can think of off the top of my head right now) so this gives blue a way, albeit soft, to permanently deal with problem creatures. It also creatures a mana-sink for your opponent since they can pay for the creatures to save them at the cost of being able to play things they wanted to after combat. Now, the major problem with this card is that it's also a mana-sink for the caster since you may end up having to dump a lot of mana into this if you're being alpha-striked. Still, it's something for theme decks to keep in their back pocket.
Pros: Blue creature destruction, kind of blue fog